>>265386261
Nother' update I'm an idiot
Correct command was:
C:\SteamLibrary\steamapps\common\SteamVR\tools\lighthouse\bin\win32\lighthouse_watchman_update.exe -D C:\SteamLibrary\steamapps\common\SteamVR\tools\lighthouse\firmware\vr_controller\archive\htc_vrc_dongle_1461100729_2016_04_19.bin
Hope this helps anyone with the same issue.