You work on it in tiny steps.
It doesn't matter what kind of intimacy we're discussing.
If it's too much, take a step back. Go to a lesser step. Keep stepping back until it's no big deal.
For example: sex.
Want to get there? Can't? Feeling all the bad feelings?
Step back.
Grope in the shower.
No?
Step back.
Kissing? Massage? Holding hands? Watching a movie together?
If you can't do anything physical, then definitely build your emotional intimacy.
Talk about deep subjects with them, build up trust, if they are capable and trustworthy.
Give a little more trust, a little more intimacy as you feel is safe and comfortable.
Some of us can't make it to certain activities anymore, due to trauma, and that's OK.
Find a partner so just wants to be with you, as a person, not as a supply. If they truly want intimacy with you, they'll take what you can give them and cherish it.
If they push or whine, they aren't worthy.
Don't measure your success by their failure to achieve intimacy. They might not be willing or capable, and that's no fault of yours.