input voltage higher than 1.8v to jetson GPIO

what would be happen i apply 5v as an input to the jetson GPIO port ?

This would destroy the hardware. You need a level converter to change this if you want a different voltage.

That will damage the port, level shift is necessary.

Can you recommend a type of a level shifter ?

I’m not where I can check my notes, but here is a very similar embedded project where level shifting should be an exact match to what you need:
http://elinux.org/BeagleBoard_Hardware_Interfacing#1.8V_I.2FO