how to map keyboard key to another key in linux 16.04

First we need to find the key code

Example When I press key "f1" then it should show "y" letter

 y  keycode ->29
 f1 keycode->67

Run the below command to get the key codes
xmodmap -pk | grep -i y  -->this will give all the occurrences of that input y

xev --->this will open a pop up when you press any key it will show the key code of it.

Use below command id to swap y letter to f1 key
xmodmap -e "keycode 67 = y"