As with a lot of early Bambu adopters, I had my main board fan fail and decided to go the Noctua route. I couldn't find a fan duct I was happy with so I created my own. 

Designed to fit on an X1C with a 35x18mm heat sink. 

Duct presses on to heat sink with built in ridges to avoid pressing it on too far.

Fan snaps into cradle and allows wires to be routed up, left, or down. 

Open on top to allow cooling to the rest of board and avoid over restricting the fan. 

This design is not based on Renba's design but uses the same fan and is installed and wired the same way.  Make sure to give them a like and download for doing the hard part.

Note:  With finesse you can replace the original fan by only removing the back cover.  After removing the back cover I disconnected the fan and gently unrouted the wire.  Then with Channellocks (yes, channellocks)I grabbed the fan and lightly rotated it up and down to break away the double sided adhesive.  This took very little force.