Your situation should be that the clutch is not completely separated, and the function of the clutch is to cut off the output of the engine. If the separation is not complete, even if the clutch is stepped on, the power of the engine will still be transmitted to the gearbox, so that no matter how the clutch is stepped on, the gear is not easy to hang. I suggest you go to a repair shop or 4s shop to adjust the free stroke of the clutch.
The other situation is even more tragic. There is a problem with the synchronizer of the transmission, which is troublesome, and the gearbox has to be disassembled.
I suggest you go to a professional maintenance agency for inspection.