To use Nike’s slogan, “Just do it!”
But seriously, what are you wanting to detach from?
If your partner is in the middle of a dysregulation, there’s not much you can do about that, and it’s better not to even be present for it. That way, without an audience, he will have to self soothe and the external chaos won’t last as long.
I think of the concept of operant conditioning. You reinforce behaviors you want and don’t give energy to behaviors you don’t want. So if he’s doing something that is unpleasant, find a reason to be elsewhere.
Many of us with BPD partners are codependents. Here’s an article that might be useful:
https://bpdfamily.com/content/codependency-codependent-relationships