I think there's lots you can do to really take advantage of this opportunity and I think it would be great to try and build up a really solid routine of the things you know work for you that you can then prioritise as and when you return to 'normal' life. For me it would be things like:
-Practice really good sleep hygiene, work out what you need in place to sleep well, things like try and go to bed and wake up at the same time each day, build time into your routine for however much sleep works for you (personally I feel best on 9 hours a day), no screen time for a period of time before sleeping, wind down before bed with a calming activities like a hot bath, reading a book etc.
-Work on your diet, not necessarily eating super-clean all the time or having to get deep into cooking elaborate meals from scratch if that isn't something you enjoy and definitely not a crash diet with the aim of losing a lot of weight quickly as that usually isn't great for your mental health. I'm talking more about eating a regular, balanced diet of foods you really enjoy, ideally incorporating lots of fruit and veg. Personally and for many people I know eating well is one of the first things to go when your mental health is suffering and it can cause lots of knock ons like lacking energy, weight gain or loss, bad skin etc. Maybe experiment with new recipes and ingredients, spices and seasonings etc to make home cooked meals delicious and appealing - are you abroad somewhere with great ingredients, exciting markets or an interesting local cuisine you can get into?
-Exercise, particularly out in the fresh air is really great for mental health, again I think it's so important that it be something you enjoy though, forcing yourself into the gym when you hate it is counter-productive and almost certainly not habit you'll be able to sustain long-term. Walking is great, lots of people enjoy zumba or dance or other group classes, or how about getting into strength training? If there's a gym that offers these things where you are maybe you could use your time to try lots of different things and see what sticks, yoga and pilates are also really great because as well as being good for you physically they have a mindful/relaxation/mental control element that can be really helpful too.
-Build time for self-care into your day, i.e. every day find small ways to really look after yourself, can be physically e.g. good skincare routine, look after your nails, hair etc or more mentally e.g. episodes of your favourite TV show, read a book and really enjoy it- it sounds so obvious but again when you are feeling down, low self-esteem, under a lot of stress these things easily fall by the wayside or even if you do have time for them you kind of feel as though you can't enjoy them properly or don't deserve this nice thing for yourself. I like to make lists of little things/small rewards for the times when my mind is blank or it seems as though there's nothing I'd enjoy, anything from nice toiletries, a coffee and cake out, a day trip or holiday somewhere I've wanted to visit, items I'd like to purchase - that way you get the triple-satisfaction of earning the reward, obtaining it, and ticking it off the list (I use the app habitica to map my daily routine and to do list and it prompts you to reward yourself at certain intervals).
-Again sounds obvious but have you thought about therapy/counselling? Since covid many therapists/counsellors offer an online option now, you could take this time to try a number of different people offering different things and see who or what you click with, perhaps looking to take this up in person when you get back to UK/home?
-Reconnect with people, personally when I'm low I really just want to isolate myself and as a shy introvert it can be really hard but I do feel it's important to have social contact and to feel part of some kind of community for strong mental health, not just for the support other people can offer you but for you to be part of other's people lives too . Again I know you maybe are physically removed from your family/friends but in a way when you've been through a period where maybe you haven't been prioritising relationships/connections it's good to start small and with virtual/remote contact. I have a policy of sending one text/WhatsApp/facebook message out per day, just asking how people are, would they like to FaceTime, how about a coffee or lunch - being brave about including people I feel really bad about having lost touch with or not replied to their messages for a while - OK yes sometimes it has been too long or people just don't get back to you or let you down or whatever but actually many people are really delighted to rekindle an old friendship. You can even expand it to making new connections (this is so hard for me but does feel good when you do it!), even very small or temporary ones like having a chat with the lady who serves you in the shop or with a co-worker. If in your 'real life' isolation has been a thing perhaps you can use this time and space to plan how to tackle that, will your work provide this, are there clubs or volunteering opportunities or networks you can establish when back home, can you start putting that in place now?