Depending on when you filed your amended return, the IRS may not see it for awhile. It takes about 4 months for amended returns to be processed. Did you put direct deposit information on your original tax return when you filed it? If you did, the IRS should be able to use the information from your original return for your stimulus check.
If you didn't have direct deposit instructions on your original return, you will need to enter that information on an IRS online portal that is expected to be opened up soon by the IRS. See this web site to follow up on when it will be available: https://www.irs.gov/newsroom/economic-impact-payments-what-you-need-to-know
