Arm animation don't work in 1.12.2 mcreator 2020.5

Hello ! I have a problem with arm animation for my custom body. I know there are a lot of topic about this subject but it don't resolve my bug. So I'm on Mcreator 2020.5 snapchot (nomally it's 2020.4) with 1.12.2 generators plugin. I made a custom armor on block bench (Bodyamror --> - body / - leftarm / - rightarm), it work the pivot point are at the good positions ! Next on mcreator I select my arm Left and arm Right and when I test, nothing work ! So if you have a custom code or something which can help me, I want it.