However, on re-reading your post, this is a course you downloaded to the watch from Komoot and you want to get it into GC. I see on my PC web login to GC that only SOME of the courses I have on my watch also show up in GC. Unfortunately, the one course I put on the watch NOT using GC DOES NOT show up on GC, so you may be out of luck. (or maybe you need to do the course so that it becomes an activity so you can re-create the course..... bit silly though.)
Perhaps you'd have more luck exporting the course from Komoot and then importing it to GC?
If anyone knows of a way to do this "watch course"->GC, I'd be interested too.