It should be obvious how to fit, so either you are missing something obvious or something is wrong that is not obviously wrong.
1. Pull the rack into the horizontal position. It might be locked into the vertical position with the shortest arm, so first make sure that is unlocked.
2. There should be three single headed arms and one double headed arm located on the top bar of the rack, close to the rear of the van.
3. For loading two bikes, push up the short arm and the medium arm to about 30 degrees above the horizontal; leaving the long arm and the double headed arm dangling vertically.
4. Load bike 1 onto the rail closest to the van, secure the wheels to the chocks with the straps and secure the crossbar with the short arm, sliding the short arm along the top bar if necessary.
5. Load bike 2 onto the rail second closest to the van facing the opposite way to bike 1. Secure the wheels and secure the medium arm to the crossbar.
Significant adjustments to the position of the arms might be required on first use, but once positioned correctly loading and unloading bikes is a doddle.
Arms can be completely removed and repositioned by opening the jaws and squeezing them closed while pulling on the arm. The plastic end secured to the rack will come off the arm (eventually) and the plastic end can then be repositioned and the arm reassembled in a new position.
Let us know how far along the stages 1-5 above you progress.
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