Hi @S_25
I have ptsd and go through stages where I have daily flashbacks. Personally, when I have flashback I struggle to engage with other people. I find I withdraw from people closet to me. Not because I don't think they would help, rather me not wanting to burden them with my problems.
I think one of the best things they have done for me is to just let me know that they are there if I need them. That they are there if I need to talk to someone or just sit with them.
I can totally understand not knowing what to do. It is a really hard position to be in, especially since people respond to having flashbacks in different ways.
I hope this helps a little.