If you already have a custom recovery like TWRP installed, you don’t need a second phone or a PC.
: Go to Settings > About Phone and tap Build Number seven times.
For maximum success on an device with no PC and no Magisk :
: Go to Settings > About Phone and tap Build Number seven times. how to root any android device without pc -magisk-
For maximum success on an device with no PC and no Magisk : If you already have a custom recovery like