I received a letter from the irs asking me for a copy of what I worked for 2019 . I don't have proof of working for that year because I didn't file . I made less than 500

I basically only have my 1099-Gs for 2020 and 2021 . I filed my 2020 on my 2021 return.  But for some reason it's asking me to prove who I am.what do I do now