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-1040x
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.