When this is true for me, I say something like "this is really hard for me to talk about, I need some help." On occasion this is all I need to say to get myself started.

T might ask, what makes it difficult to talk about? And I might say fear that you might judge me or I am ashamed or I am afraid of what it will feel like to say it out loud.

T might then ask, is this one of those things that you want me to push you on (I have previously asked him not to "let" me avoid things that I mention), or do you need me to back off. For me, it is much worse to avoid than to be pushed forward.

So in my experience, when I let T know it's hard for me to talk about, it just organically flows from there. Sometimes we spend the whole session talking about talking about it.