Yes, you can appeal, but it depends on the facts and circumstances. As @macuser_22 said, probably the IRS changed something else, which indirectly changed EIC also, and you need to figure out what that was.
For example, suppose you had a GoFundMe campaign to pay medical expenses, and GFM sent a 1099-K. That's not taxable income because it's a gift, but the IRS might have determined it should have been taxable, which disqualified you from EIC. Your response to the IRS letter would be a letter of explanation as to why the 1099-K was not taxable income and including documentation and other proof that the campaign was a gift.
Or, for example you might have forgotten to include unemployment compensation, and when the IRS added it, you were disqualified from EIC.
Or, someone used your SSN fraudulently on a 1099 so the IRS thinks you had more income.
You need to carefully analyze the IRS letter that explains the EIC adjustment. You may be able to get more information, especially about additional income that was added to your account, by getting a Wage and Income transcript from your IRS account.
https://www.irs.gov/individuals/get-transcript
