Loosen the clamp bolts that hold the front idler yoke tight on the adjusting screw and then back the screw off to pull the front idler back as far as possible.
Then jack up the back of the machine and drag/lever the track under the sprocket and also get the track laid out straight under the track rollers if it is off to the inside too. Set the tractor back down on the track.
Work the track onto the sprocket all the way around, perhaps by driving forward gently. Do not go so far as to run off the track again.
You can also hook a chain or come-a-long to the front of the track on the ground and pull it straight out under the idler so it's easier to stay on it as you ease forward.
Once you get the track on the sprocket completely, put the track on the bottom of the front idler (perhaps press down with the dozer blade and get the idler off the track to make this possible)and then while pulling sideways/forward with a chain connected to the track at the top of the front idler, or levering with a bar (be very careful so it doesn't hurt you as you move the tractor) gently back the tractor up and the track should come back onto the idler.
Tighten the track and retighten the clamping bolts.
Easy😆