To become an expert in UI/UX designer one must have to follow the below steps:-
Learn all the fundamentals of basic terms in designing through books, internet
Choose any online course or Bootcamp
Design interfaces thoroughly
Join any internship to develop your skills
Even without having any knowledge about this UI/UX design also one become a professional in this field if learned from a right place for that I recommend you go for the UI/UX certification course offered by Intellipaat includes training and certification, and it serves as a key predictor of your skill.
Before that, watch this free tutorial video from Intellipaat if you're interested in learning more about it