How do you put a track back on a komatsu excavator?

This should work on most mid-size excavators:

Slacken off the track adjuster screw and push the idler back to a fully retracted position. If the track is worn you may be able to man-handle it back into position over the sprocket and idler and then readjust the track with grease.

If that is not possible, you might have to press out the master pin that holds the track together then wrap the track over the idler and press the pin back in.

The master pin has a dimple in the centre which helps identify it, these are very tight and special tooling is required to replace them easily.