You shouldn't deal with the 2018 wages and taxes withheld on your 2020 return. This should be dealt with on your 2018 return.
If you received a W-2 for 2018 and the amount of wages paid was incorrect, you should start by contacting your employer for a corrected form.
The IRS offers the following advice if you haven't received your W-2s: [IRS Topic 154 - Form W-2 and Form 1099-R (What to Do if Incorrect or Not Received)]
1. Contact your employer/payer.
2. If you still haven't received the missing or corrected form by the end of February, you may call the IRS at 800-829-1040. (See Telephone and Local Assistance for hours of operation).Have the following information handy:
- Your name, address (including ZIP code), phone number, taxpayer identification number, and dates of employment,
- Your employer/payer's name, address (including ZIP code), and phone number,
- If known, your employer/payer's identification number.
3. The IRS will contact the employer/payer for you and request the missing or corrected form.The IRS will also send you a Form 4852, Substitute for Form W-2, Wage and Tax Statement, or Form 1099-R, Distributions From Pensions, Annuities, Retirement or Profit-Sharing Plans, IRAs, Insurance Contracts, etc. (PDF), along with a letter containing instructions for you.
If you don't receive the missing or corrected form in sufficient time to file your tax return, you may use Form 4852 to complete your return. You'll estimate your wages or payments made to you and taxes withheld on Form 4852. Please see this article: How do I file a substitute W-2 using Form 4852?
