Welcome to this forum @asp,
Koen De Vleeschauwer, the author of the ThetheredCam device adapter that you are trying to use, is no longer actively supporting this device adapter. Many years ago, I tried using it with the Canon DSLR that I used to have, and found that it kind a worked, but did not end up to be very useful. One detail I noted on the TetheredCam - Micro-Manager page, is that it is 32-bits only, which means that you need to install a 32-bit version of Micro-Manager. If that is indeed what you are using, I have no suggestions other following the instructions to the letter, and if it still does not work, we should a note to that page to warn others.