Well, you have the good wishes of countless readers of your thread!
Congratulations on your birthday! 🎉🎂🎈🍾
As for how to cheer yourself up - d’you want going out or staying in suggestions?
You could spend the day cosily planning a grand day out for sometime soon.
You could download a book you’ve always meant to read to your kindle, phone app, wherever, open a bottle of wine …
Send a nice chatty email to someone you’ve fallen out of contact with.
Binge watch something amazing like Succession, or I May Destroy You, or whatever.
Walk somewhere for an indulgent lunch.
Decide what you’d like to be doing on your next birthday (if different) and set things in motion to make it happen?