This might be obvious, but there are tons of writing prompts out there, and if you commit to doing them regularly, even if they're short, you'll start getting your flow back. (If anyone knows a good source, add it below!) It's nice to have the choice of topic made for you, so you don't end up feeling attached to much about it, although you might surprise yourself with what you come up with. I started a weekly virtual group a while back to do exercises as a communal accountability thing, and that really got me excited about writing again. Morning pages were also something mentioned here a while ago.
Basically anything that gets you into the technical habit of writing, so when you want to write about something specific, you'll be practiced and ready! I have found that inspiration has an easier time breaking through to the page when I'm not as rusty. Also, unless you want to submit a piece to a publication that fits a certain guideline, there are no rules. The fewer boxes you try to fit yourself into, the easier it flows!