I hope you are able to talk about it. The very first time I mentioned it, kind of out of the blue after a few sessions, I said "I've been cutting myself a lot recently...Well, not just recently but doing it more lately." This was after a lot of silence, saying I had something that was hard to say and she said "In your own time." It was very difficult but a couple of years later I can mention cutting without feeling that terrible shame.

You might find it easier to write it down, or look at something else while talking. You could say you feel the need to do something physical when feeling distress. Or just say "hurt yourself." The first time is the hardest. But your T won't judge. They will just ask you practical things about how long it has been happening, how often, the extent of it, if anyone else knows etc. You may feel overwhelmed at first. But it will soon feel okay to talk about it. I wish you the best of luck.