am unsure of exactly how your tractor works, on mine, there is a 4wd engage lever near the driver's left heel.
This lever is moved up or down to change status. For a while, I struggled getting into and out of 4wd UNTIL I learned to simultaneously put gentle pressure on the lever, press clutch in, ROTATE STEERING WHEEL FROM STOP TO STOP (right to left or l to r). Somewhere during the steering wheel rotation, the lever EASILY drops into 4wd. All the while, there is no forward or rearward motion required of the tractor.
Why not give this approach a try and see how it works.