This is very small, fairly easy to print jig that requires 32 gauge wire (~0.3mm diameter). Pause the print at 1.5mm layer height and force some wire into the slot. I recommend adding some superglue to the wire after the print has finished. The ends of the wire should also be bent up and down to push it up against the Joycon connector, without damaging the pads. It should be slightly springy.

This model is a redesign/alteration/remix of the RCM Jig designed by yahnbaron. https://www.thingiverse.com/thing:2892320