How can I use AI to create a variable?

I have step where I ask a user for their username and the response I got was something along the lines of "pretendUsername is my username but i guess i didnt set up an email with my account"

I obviously don't want that entire string to be set in my username variable. Is there a way that I can have ai understand that pretendUsernamepretendUsername IS the username that needs to be used in the usernameusername variable?