Duplicate nicknames

Hi,

Do you know if there is a way, how to avoid duplicate nicknames for users?
What I want to achieve is that one user will have reserved one nickname, and the other user will not have the right to use the same one, and he will need to use a different one.
I hope that the explanation is clear.

Thanks for any advice,
Jakub

Have a look at Nayeli (Code Queen) tutorial here.
https://codequeen.wixsite.com/membership-dashboard
https://www.youtube.com/watch?v=yLCOqsVHhD0&feature=player_embedded

Thank you.