Claim as PAYE for job Expenses for the last 4 years

Hi, I've been trying to claim for job expenses for the past 4 years as I have read in the guidance and it is possible to do it. However, I'm not sure how to do it as I normally complete the Self Assessment every year but I have never thought that I could claim expenses on my job. Is there a way to reopen the previous self-assessments and declare them this way? Or there is a different way to do it? Any help will be highly appreciated. Many thanks 

Hi, 
 

You will need to write to HMRC to amend returns prior to 21/22 as they are outside the 12 month amendment window. Please see : Self Assessment tax returns     . Thank you.