You can either amend your return now or wait for the IRS to send you an automated notice letter proposing an increase in taxes due to the unreported income. You can, then, agree to the changes and pay the difference in tax.
If you decide to amend your federal return, then you should amend your state returns as well. Please follow the directions in the TurboTax FAQ below to prepare your 2018 amended returns.
https://ttlc.intuit.com/replies/3288565
Note: You will need to mail the completed returns. An amended return is not eligible for e-file.