If you did not report the income from that 1099-K on your tax return, then yes you will need to amend that return to include that 1099-K money.
If you did report that income but did not state it was from a 1099-K, that's OK, you do not need to amend because the IRS receives the same information you do (as long as the total income is reported on your return).
I have added directions below on how to both amend that return and how to enter that 1099-K.
AMEND RETURN
https://ttlc.intuit.com/replies/3288565
HOW TO ENTER 1099-K
https://ttlc.intuit.com/replies/5108144
