This is a 3d-printed pogo-pin programming jig for Tomu (https://tomu.im/), a tiny USB device. Normally you can use the built-in USB bootloader to reprogram it, but in the cases where you can't, having a jig to align the SWD programming pins on the bottom can help.
To build this jig you will need:
Also handy is a small USB hub with per-port power switches, like this 4-port Sabrent USB hub
When soldering the pogo pins, make sure they poke out about 1.5mm from the 3d-printed base.