Tools required: Two 4mm allen
It is imperative to apply blue loc-tite to both the nut and bolt when reinstalling.
The nut requires a 4mm allen, while your bolt also uses a 4mm allen. Loosen the nut from the bolt. It may be easier to loosen the nut if you apply downward pressure on the handle with your forearm like in the picture.
By taking some of the load off of the nut/bolt it is easier to unthread. Notice when removing your elastomers how they sit in your FlexxMTB. It is important to install them with small side into the handle and the round side against the center section. Orientate the elastomer so the bolt hole does not protrude from the handle or center section. It's important for the bolt and nut to have interference from the elastomer.
With the elastomer in place install the nut with the rebound elastomer on it. The radius'd side of the rebound elastomer should be facing out with the square side against the handle. From the center section the it should look like this:
Now install the bolt, ensure there is blue loc-tite on both the nut and bolt threads. As when removing the elastomer it can be easier to turn the nut if pressure is applied downward through the handle unloading the tension on the bolt/nut from the elastomer. Tighten the nut until the bolt bottoms out. With the bolt bottomed out in the nut the bar will have 5* of up sweep.