was your "employer" withholding FICA and medicare taxes? if yes, then you should have gotten a W-2. if not, then it was treating you as an independent contractor in which case if you were paid over $600 it should have sent you form 1099-NEC. you file as self-employed using schedule C - can't use the free edition.
you need to contact them to find out and request a replacement w-2 if an employee or 1099-NEC if an independent contractor.
if they won't then you need to use form 4852
the IRS says you must take the following steps before filing Form 4852
• Attempt to get your Form W-2, Form W-2c from your employer
• If you don’t receive the missing or corrected form from your employer you may call the IRS at
800-829-1040 for assistance. You must provide your name, address (including ZIP code), phone number, social security number, and dates of employment. You must also provide your employer’s or payer’s name, address (including ZIP code), and phone number. The IRS will contact your employer or payer and request the missing form. Getting through to the IRS may be difficult be their phone system is constantly overloaded
try calling on several days and if you can't get through use the form
