As schmjoe mentioned check their support site. They also have a forum there for assistance from other members. The directions they provide are very minimal. Seems it might be based on Garmin as it was years ago. I signed up for a trial account to test it out. Just using the web interface to link my Garmin with nutracheck.
Log in to nutracheck
Click on Profile, link devices and apps
In the Garmin section, click on Link Accounts (or unlink to toggle it off, then on)
Follow the prompts to link your Garmin account with nutracheck
