Ah, classic one that. Happens to the best of us, mate. A slipped track usually means you’ve hit a bit of uneven ground or had the tension set a touch loose. First thing, lift the side that’s slipped off just enough so the track can move freely. You can use your boom and blade to balance it, but make sure it’s stable before you start. Next, find the grease valve on the track adjuster and carefully let a bit of grease out. That’ll loosen the tension so you’ve got some play to work with.
Once it’s roughly in place, fire the machine up and slowly roll the track while someone keeps an eye on it. It should walk itself back on with a bit of patience. When it’s seated properly, pump the grease back in until there’s just a bit of sag in the middle. If it keeps slipping off, it might be worth checking your bottom rollers or sprocket wear. Sometimes that’s the real culprit.