Incorrectly filed taxes

Hello everyone, long time reader and first time poster in this sub. So as everyone knows it’s tax season and my boyfriend decided to do his taxes about a month ago. Got through it all good but when we saw the estimate for the amount of money he was getting back I thought it was way lower than it should be and he also owed quite a bit to the state. So last week, I filed mine and he asked why said I don’t have anyone that can claim me as a dependent. I told him because I’m not dependent on anyone for pretty much everything through out the year. He was under the impression that he could still be claimed as a dependent by his mom. Not sure why since she lives out of state and he has his own apartment and supports himself. After he asked me, it clicked that he probably filed himself as a dependent or rather that someone can claim him as a dependent. So I’ve been reading online you can amend taxes and get this fixed. But he’s already gotten his tax check and received his money. If he fixes it, will they be sending more money once it’s processed or would it be something he’s got to wait until next year for? He filed on TurboTax so now I’m wondering what the best way to go about fixing it would be. Thanks for reading!