ITR filing for 3 years

Hi, I have been working since 2018 and my CTC is below 5 L for the first 2 years and above 5LPA at present. My question here is I have never cared or was not aware of filing ITR as my CTC was below 5LPA for the first 2 years and one my friend said its not mandatory if its below 5LPA, but at present since my salary is above 5LPA I know I should file ITR, But before doing that I wanted to make sure about the ITR for the first 2 years is not mandatory, is it mandatory to file all 3 years if so I have missed it and what should I do now? I am a complete newbie in the tax field..