In the courses and classes step of Importing a timetable from TimeTabler, you map your subjects in TimeTabler to Arbor.
If you're unable to match any subjects and it says they will all be imported, the most suitable resolution will depend on when you're doing the import.
If you're importing a timetable mid-year, this might be because the names do not match between TimeTabler and Arbor.
Click the red Cancel button on this page, stopping this import. Rename your courses and classes, then start the import afresh.
Importing a timetable for next year
If you're importing a timetable for next year, you can just import them all. The difference in name will not impact the import, as you won't have subjects next year to match them to yet.
If you need to make changes to the course names after, you can do this from School > Programmes > Year Courses.