Remove the lift and hold lever assembly using the 17mm spanner (wrench) to undo the pivot bolt.
Use the 4mm Allen (hex) key to remove the dome headed screw and locking washer holding on the plastic wheel, this could be a tight fitting on the foot of the handle and need prying off carefully.
Replace the plastic wheel ensuring it is fitted on its mounting boss the correct way round, replace and tighten the screw, not forgetting the locking washer.