'IF I WERE YOU I WILL...' people user WERE instead of WAS...

Hi, I want to ask you why in “IF I WERE YOU I WILL …” people use WERE instead of WAS. Is not “IF I WAS YOU I WILL …” more proper? because I followes by WAS and YOU follows by WERE.
Thank you.

You seem confused. It has nothing to do with the pronouns, and there is no ‘will’ involved. The available forms are:

If I/he/they were you, I/he/they would (polite, formal)-- This is the subjunctive and all persons take ‘were’

If I was / he was / they were you, I/he/they would (casual, still unacceptable in careful English)– This is the indicative and the personal pronouns each take the appropriate form of ‘be’.