Practice.
It's a cognitive behavior. Like any behavior, it may be too difficult for you to do the behavior right now, but you have to start somewhere. Think of it like a training montage in a movie.
Pick a trope that resonates with you: recovering the ability to walk after a major car accident or stroke, or losing a huge amount of weight, or whatever.
You have to get up every day and make an attempt to not care what other people think of you. And you will fail sometimes. Some days you'll barely be out of bed before you are overcome with emotion about it.
But commit yourself to the goal, practice it, and eventually you'll start to notice you can stop caring about what some people think of you sometimes.
And by that point, you're already well along in your journey.
What you're going through cannot possibly be easy. When I was in recovery, it was a young child so I didn't have to function out in the world, so I can't even imagine how much harder it must be for you. But I trust you and your ability to learn this skill. The fact that you're up and doing things, that you're actively recovering, is evidence that you have the strength, the will, and the tenacity to move past this pain and create the boundaries you need to thrive.
I wish for you health, recovery, strength, comfort, and all of the growth and wisdom that you can find on the way there.