You can change a release date once a release has already been distributed. The basic principle is to just redeliver the release with the new release date (this is technically called the "start date").

Note that if the release is still in delivery, you may need to pause the delivery: How to edit a Release that is still in delivery.

Here are the steps for changing the start date:

  1. Click on Assets > Music
  2. Click on the asset you'd like to edit the release date of.
  3. Select "distribution" from the menu on the sidebar (see image below)
  4. Click the big purple Distribute All button on the top right corner of your page
  5. Scroll to the bottom to find the "Release start date" field and edit it there.