He'll normally start by trying to get my attention by saying my name like "hey ........ you okay?" If that works he will ask where I was, then go on to ask vague stuff like what can I see, then He'll make it more specific and ask something like what colour is his t-shirt, what can i hear and bring me back to the room.
If it's gone further or it's turning into a full dissociative flashback he'll use touch, he'll touch me gently on the arm, talking to me asking me if i can hear or feel him.
He was there for the event that caused me the most issues so has an understanding of what to avoid, and what can help. Eg feeling warm, softly spoken tones. If I can respond then he'll use the same as above to guide me back. If his phone is near by or we're at home he'll put music on that I like, things like that.
If it goes as far as to be completely gone, or i shut down he just stays with me through it, keeps talking to me, using gentle touch, comforting me through the process. I tend to get a drop in body temp so he'll grab a blanket or hot water bottle. If I can find words he'll encourage me to talk about what is happening or I'm seeing and feeling, and he'll use those things to challenge them and remind me I am not back there.
Hope all that makes sense! Feel free to reach out if you want me to go into more detail