Personally this is what i have found helped students of mine who found trills troublesome.With trills it might be good to take just two notes and do stuff like thiseg: play: CDC - what does this feel like. One turn CDCDC - how does 2 turns feel? Try not to count the number of times you hit a note, instead listen to the sound produced and effect on the hand. keep increasing.
It would be helpful to explore all the Ornamentations. Start with the simple ones then tie them together. The important part is that you are not counting or watching the notes, instead you close the eyes and feel the movement in the hand, listen to the sound duration. IF the fingers physically fail, then you need to use standard finger excersise, like Hanon etc.