I fly my ac then weak gps signal and my ac started moving itself
What to do?
I was flying indoor

The building was blocking GPS signal reception for your Phantom.
Your Phantom did not move by itself.
You lose GPS and your Phantom will be in atti mode, drifting with no position holding and with no brakes.

What to do?
Don't fly indoors

You were told this yesterday when you asked the same questions.
And now you are posting twice more ?