If you've already uploaded a recording to your account and need to associate it to a Release, there are 2 ways in which you can do so:
Via the song the recording is associated to
Note: the recording must be marked as a Master in order to associate it to a Release.
1. Open the song project that the recording is associated to.
2. Click the "more" / ... button next to the recording.
3. Click Edit recording...
4. Scroll down to the Release information section.
5. In the Select Release field, type the name of the Release.
6. Click on the corresponding existing Release name or click Create to create a new one.
7. Click Save in the Release information section to apply the Release.
8. Click Save at the bottom of the recording edit modal to save your changes.
Via the Release
1. Go the Releases tab of the catalog or playlist folder that you're in.
2. Double-click the Release to open it.
3. Click Edit.
4. Click + in the Tracks section.
5. Select the source that you'd like to pull the recording in from. If it's already in your catalog, select Catalog.
6. Search for the recording you want to associate to the Release.
7. Click on the corresponding recording.
8. Click Continue.
9. Click Add Recordings.