For use with Gil Tesa USB Type C rechargeable battery mod
https://retrogamerepairshop.com/collections/gbp-power/products/game-boy-pocket-usb-c-battery-mod
https://www.youtube.com/watch?v=3qAQNfZgSRI
(usage of jig not shown in video)
Print jig and snap on to DISASSEMBLED top shell housing for Game Boy Pocket. Should fit all shells but may fit others better than some. Use (round) needle files to cut port hole out little at a time following the contour of the jig. Remove material slowly and check fit frequently. Finish with flat needle file to smooth out bottom of port.
Better files may work better but for $5, it's hard to complain about these: https://www.harborfreight.com/12-piece-precision-needle-file-set-4614.html
The author hasn't provided the model origin yet.