Anthony has written a one page on how to heal/recover from PTSD. It has some good points.
Skills I would suggest to develop to be more present in your life include: emotional regulation, breathing, meditation, relaxation, exercise, mindfulness, sleep hygiene and a commitment not to beat yourself up for being stuck in the state that you find yourself in. I have wasted a few years beating myself up over things. Still had to do the same work at the end of that. (I hope that is the end.)
DBT and CBT are good to look up and start being aware of and choose one thing to do for 5 minutes per day. Do that.
It won't go away in a day or even a few weeks. It will take time and persistence, patience, perseverance and practice.
So developing self compassion is also important in my mind. You have to be kind to yourself and begin to work on your own emotional boundaries so you can self regulate to shift the depersonalisation.
Finding fun and self soothing are really important there has to be stuff to look forward to and a reason to actually be present in this now. If it is just more scary stuff you won't shift out of it.
Still on my L's with this stuff. You know the beginner's mind in meditation, life skills etc.
Best Wishes to you with all that.