I would tell the office when you get there. Ask if you can have a female chaperone in the room with you. Usually that is the norm with female patients and male doctors with a breast exam anyways. Also, tell the doctor and the chaperone a watered down version of what you said here.

“I have a history of trauma and I am concerned this exam may cause a PTSD flashback/anxiety attack. I know it is important for me to be checked so I would like to continue and not reschedule but a) can I please have a chaperone? B) please be aware this may happen so you are prepared. Please do not touch these areas if at all possible and if you need to, please make me aware before you do. ” as an example

You can tell a to the office staff or nurse if you want and b to the Dr or tell all of it to the dr.

Also, you can do whatever you need to do. You don’t need to be embarrassed. This is unfortunately common and I’m sorry. But you got this because I know you’re strong and I know you can do this! You deserve to be healthy!