You should not amend your return at this time. You should wait for the IRS to process your return. More than likely, the IRS will catch the omission, as your return won't agree with their records. They will then send you a letter with proposed changes to your return. If you agree with the changes, you won't have to do anything. If you don't agree, you will have to respond to the IRS. Because your return as filed will not agree with the IRS records, you can expect delays in your return being processed.
In the event the IRS does not catch your omission and credits you with the Recovery Rebate Credit for the stimulus you already received, you will then want to file an amended return.