The stimulus is a credit on your 2021 return. The IRS was instructed to make payments early based on the best information they had, knowing it would sometimes be wrong. Your dependent would not have gotten a check on their own unless they were not a dependent for 2020 or 2019.
If they were legitimately not a dependent in 2019 or 2020 and got a check, but are legitimately a dependent for 2021, then you will be entitled to another rebate on your tax return, and they will not have to repay their check. Only indicate what you received under your name.
