Cut the part of 1 pist

I can’t cut a part of just one pist, I have to cut all the pists. Before when I wanted to cut a pist that was easy but now I can’t, I don’t know why, Need help !! Maybe I did a bad manipulation tell me ! (I can see clock on all the pists when I try to cut)

Turn off “Sync Lock” (at the bottom of the “Tracks” menu:

Thanks you !!!