Player Developement

[IbrahimMirza25]

I play FIFA 20 career mode with Neymar Jr. and was loaned to Napoli by PSG. I try to go on player development and train myself, but once I've selected 4 training sessions, all the training sessions are locked. Because of this, I can't fill my 5th training slot and am not able to improve my player. Can you tell me what I should do to solve this?