You amend the tax return that was filed to make any changes.
See this TurboTax support FAQ for amending a tax return - https://ttlc.intuit.com/turbotax-support/en-us/help-article/tax-return/amend-change-correct-return-already-filed/L4VjJ9BA2_US_en_US?uid=ld1n99kr
What year...previous tax form? By earnings do you mean your refund? What do you need to change to get your refund?