Hello smokepurpl
Unfortunately, if you submit players into an sbc, they are gone forever, and there is nothing that can be done about it. It is best to slow down and pay close attention to the squad before pressing submit.
As for players that were on the bench, you should still have them, as those players are not submitted along with the on the pitch squad.
If your players were accidentally sold, then you should be able to utilize quick sell recovery. But be aware, there is a limit, so if you lost more than 5 players that you wanted to keep, you will have to prioritize and make sure that you recover the 5 that are most important to your club, or have the highest value and cannot easily be replaced.
Again, please be careful and don't rush when crafting sbcs.
All the best to you!