Try lying on the floor with your bottom on the wall, and stretch your legs up the wall. As if you were sitting on the wall. Put a book or a thin pillow under your head for your comfort, and just rest there for 10-15min. Read a book, listen to some music, plan your jobs for the day, whatever. Do this once or twice every day. More often, if you like. You can also stretch your calves and hamstrings this way. They tend to tighten when your legs swell. Once you've got comfortable with your legs up, flex your toes down towards your face. You will feel the stretch in your calves.
At work, try to get up and move around frequently. Keep a spiky foot roller under your desk and roll your feet on it. I have this set https://amzn.eu/d/02O4jQF8 the peanut is my favourite - I even took it on holiday with me.
Can you wear trainers to work? The mesh sort with good ventilation. I'd put a sports orthotic inside as well, to support your feet in a healthy neutral position. If you have to wear formal shoes, and cannot get a medical exemption, slip them off whenever you sit at any desk or table and roll your feet around. Make big circles in both directions from the ankle, flex your toes up and point your feet. Roll them on a foot roller. If there's a way to keep thinkgs cold at work, put an icepack on the floor and rest your bare feet on it. This one really does keep cold longer than any other I've had https://amzn.eu/d/0fyAoNg2
Sleep with your legs raised. And cooled, in this heat. Use a spikey roller and ice packs at home as well as at work.
Wrap icepacks in a towel when you use them so that you don't get freezer burn or chilblains!
If you wear socks, make sure that they are at least 70% cotton or viscose, and that they do not dig in anywhere. This year my calves swell in the heat for the first time, and I find that trainer socks are better than ankle socks as they don't dig in when my calves swell. There are socks designed with soft tops to prevent digging in if legs swell. I don't know how this translates to swelling feet, but definitely you don't want anything that digs in and prevents fluid leaving your feet.
Moisturise, especially if you already have dry skin or are post-menopause. Dry skin doesn't stretch well and swelling can damage it and make it split, putting you at risk of cellulitis. And the splitting can be painful.