If a W-2 was issued, even for a few days work, you should report it on your return (i.e. file it).
Are you sure a Form W-2 was issued for the few days work you did, or was only a couple of days at the end of 2020 and you continued to work for them in 2021? (Most employers do not add workers to their payroll system if only a few days work is involved).
If, however, you believe a W-2 was issued, you should contact the employer and ask for yours. If you are unable to contact the employer or they refuse your request, you can complete a Substitute W-2 (Form 4852).
For instructions, see How do I file a substitute W-2 using Form 4852?
