how to remount in rw in twrp ?Restoring persist isn't supposed to be possible through TWRP. It's only there to backup for manual restoration if needed in an emergency. That being said, the current backup for persist backs it up as files and not an image, so you'd have to tar extract the backup to /persist after manually remounting it rw in TWRP.
I'm adjusting TWRP to backup Persist as an image to make it easily restorable via dd, but your existing backup can still be used.