So I found some stuff here but it seems incomplete:
Is that on your old Mac or new mac?
Another place to look is
/Library/Application Support/GarageBand/Apple Loops/
Some Jam Packs installed previously there loops there.
And you may need to transfer the Instrument Library as well:
/Library/Application Support/GarageBand/Instrument Library/
In fact, you have to make sure you transfer everything in /Library/Application Support/GarageBand/ that might be missing.
After adding all loops again, rebuild the Loop Index, see:
Which of the steps in the support article do you need help with?
Basically you need to
- delete all Loop Index file, so that your loops will not appear as duplicates in the loop browser.
- Locate all library folders that contain loops.
- Drag these folders onto the loop browser.
But ask, which steps from the article we need to explain better.
I think, HangTime has a better description in the "Bullets&Bones" FAQ, but I cannot find it right now. My Internet is not very reliable at the moment.