p4 add <new file>
cp <old file> <new file>
p4 delete <old file>
p4 submit

That how you tell someone “GO TO HELL!” in perforce commands.

i only know git, so why?

You can do ‘p4 rename <old file> <new file>’ instead and maintain file history for <old file> when you filelog <new file> and reduce difficulty integrating this change into branches/streams.

AKA it’s a fuckwitz move to rename a file in perforce and not use ‘p4 rename’