Today, as a place to start your writing, think about a way in which you are beating yourself up or otherwise torturing yourself with worry or negative self-talk, and write into that fear/despair/anxiety with the aim of poking holes in its logic.
If it’s helpful, perhaps make a little list of ways your are being hard on yourself, pick one of them and write to back up the feelings swirling around just that one thing. And, if you need help deciding which thing on the list to write about, try the one on which you feel the absolute least willing to cut yourself some slack.