Please familiarize yourself on how to ask a health-related question in a way that'd be potentially helpful to your fish and to you (please see links below). The less info you give us, the less of a chance we can say anything helpful or even sensible.
I have observed countless number of threads lacking details that are required to make a proper diagnosis involving fish health. For this, I am building up this thread with diagnostics for you to determine what is wrong with your fish. More details of other health issues can be found here...
In my 50+ years of helping hobbyists in keeping their fish healthy and happy it's often not easy after hearing input like; "My fish died. What happened? No, I didn't take the 2 seconds needed to check the temperature. I've thought of buying a test kit but never got around to it. But, I know...
my redtail catfish ate normally, it was just that the frozen food was expired. After I gave him new frozen food he accepted it and was healthy again. But after some time in the morning I saw that the redtail's upper fin was ripped and first I thought it was a disease but then I saw the gar trying to eat him. I moved the redtail catfish in another tank but he refuses to eat and spit out all the food that was in his stomach earlier. WHAT IS HAPPENING?????
So your red tail was getting beat up, which is stressful for the little guy. Then you move him to another tank to be away from the gar, good move, but moving tanks can also be stressful for fish. So he's got stressed from two issues, the bullying and the moving. RTC's are renowned for regurgitating their stomach contents when stressed.
I'd let him settle in his new tank with lights off for a while. Maybe add some salt to help with his injury and don't try and force the feeding issue, he'll eat when ready.
Most important, keep that water clean and stable parameter wise to prevent stressing him even more.