I worked up to it by living in a dorm with no air conditioning this past spring quarter. As in to say, only heat stroke could get me to be shirtless all the time in front of my SO. Out of necessity, I am sometimes able to mentally frame my chest as a male chest. I found that, for me, the fact that it is legally and socially taboo for me to be shirtless adds to my dysphoria. And so, me being able to be shirtless and it not be a big social deal has been good. I'm only that comfortable with my SO though, because I know she always sees me as male regardless of my chest. Of course, sometimes I hate my chest enough to wear a binder even in the dorm on a hot day, so it's hit or miss depending on the dysphoria forecast for the day. I realize that I am more okay with my chest more often than most guys though, so this is just my own experience.
So I guess my advice would be to ease into it with trusted friends you know always fully respect your identity, focus on how manly it is for it to be socially acceptable for you to be topless, and to have an "escape plan" if it's too uncomfortable. If you aren't comfortable with it though in any context, maybe you shouldn't force yourself.