On the left of the key where you place your left thumb are two keys that are next to each other. If you look at it I believe there are two screws? On my flute, the left one does not have a screw causing it to stay there. When I press the button that causes it to raise, it just stays there while the one on the right goes down normally. I`m wondering how much would it cost to repair this? Thanks.

It would probably be really cheap

It depends on what level you are playing at. Those keys are only used for trills and the high notes. It doesn`t seem like a very high level (about school level) because of the name you gave to them (they`re actually called trill keys) so it doesn`t matter, but if you accidentally hit the D# trill key (the one you`re talking about) it will leak air, which will cause problems. Just lift it up yourself with your index finger if it does happen. Get it repaired though, but for a whole new screw you might have to order it. It should be a fairly small and cheap one, because some of them are huge, lengthwise. If you are renting one, which is the better thing to do, just get it exchanged. It`s not worth the wait if it needs to be ordered. And check that all screws and springs are present! And if you own it, good luck to you.