Discord bot for randomly choosing a person in a text channel

I made a discord bot using discord.js and it has some useful commands to it. I want to add one more , one that will tag a random person from the text channel i used that command. For example if i use that command in #test123 channel , it will tag a random person that has test123 as a role . Any ideas? ( I am new to java programming and i have a little bit of trouble making this work )