For your Federal amended return (1040X):

Where to File Addresses for Taxpayers and Tax Professionals Filing Form 1040X

https://www.irs.gov/filing/where-to-file-addresses-for-taxpayers-and-tax-professionals-filing-form-1...

If you have a State amended return, you can check your State's website for their address.

Also, an instruction sheet should print with the mailing address for the amended returns.