I found a solution after unscrewing the drill and disassembling the mechanism from the inside, the shaft ends with something like a torx (an allen but it looks like an asterisk it is probably called a torks), it fits perfectly with a socket wrench, so I had to counter it, the problem was solved. But then I had to put together these puzzles all the gears, I washed everything in a solvent, greased it and put it together. Thanks a lot for your help.