SuperMarketInformation about that can be found here: https://github.com/tmk/tmk_keyboard#magic-commands
If I understand it correctly, you have to hold down LShift+RShift while plugging the board in, and then hold down Space and press ~ . After that you need to hold Space again and press B to boot the board, then you should be good to go.
SuperMarketCheck out hid_listen then and see whether you can find a bootmagic comand in there: https://www.pjrc.com/teensy/hid_listen.html
After starting hid_listen, press Lshift+Rshift+H to see a list of commands (always in combination with Lshift+Rshift). Or, you could just reprogram the board yourself with TMK or QMK.