How to convert Unix time to WordPress date format

Hi there

I’m trying to import an old CMS into WordPress and I cannot figure out how to convert the original unixtime which is expressed as seconds since 1970 to WordPress date format: yyyy-mm-dd.

I’ve searched high and low haven’t found anything that will work for me. I’m not proficient at php programming so some of what I’ve found isn’t working for me.

I’ve imported everything into an xls file but getting the time converted is the only thing holding me up.

Does anyone have a solution that will work for a non-programmer?

thanks in advance.
G