I often had the problem that I could not insert the filament quicky.
I did not manage to find the hole of the bowden coupler although I cut the filament with a 45° angle and twisted it a bit.
So often I disassembled the bowden coupler, inserted the filament and then but the coupler over the new filament.
This is now the solution so you do not need a tool for it.
Should fit for all couplers with wrench size 8.
Assembly: Disassemble the bowden coupler, remove the black plastic washer, push the printed part on it so that there is enough space to the extruder later on, reinstall washer, reinstall coupler. Done.
With 0.3 res it even prints in 10 minutes.