To tighten collet to the shaft you need to hold the armature and use a wrench to tighten the collet to the shaft.
To get at the armature you need to take the router apart
1) removing the brushes from the top side. Identify which brush goes where as you remove. You need to place them back in the same place the same way.
2) next remove the 4 screws on the collet side of the router then take apart the casting from the plastic body.
3) secure the armature and tighten the collet on the shaft.
4) rebuild the router.
Service centers can do this as well if your not comfortable.
To get at the armature you need to take the router apart
1) removing the brushes from the top side. Identify which brush goes where as you remove. You need to place them back in the same place the same way.
2) next remove the 4 screws on the collet side of the router then take apart the casting from the plastic body.
3) secure the armature and tighten the collet on the shaft.
4) rebuild the router.
Service centers can do this as well if your not comfortable.