It's a simple part to replace the pneufit of BMG extruders.
You will need a M4 nut and a 2mm drill bit.
Instructions:
Once the nut is installed, screw the bowden into the adapter without exceedeng the nut or as like the picture (for better filament guiding once installed).
Drill the bowden end on the lenght of the part, and test that the filament correctly slides inside.
If you prefer to overpass the nut, you will need to unscrew the bowden to place the part and screw it once in place, it will place the bowden into the extruder housing.