Refer to this guide on Price Indexation for an overview of this feature.
Reversal of indexation will need to be a manual adjustment. The steps outlined would be as follows:

  1. Delete the Indexation Change Logs / Scheduled Change Logs. These are marked with a special field, so these ones are easily identifiable.
  2. Change the Selling Price / Cost Price on the Subscription back to the original value.

This will work if there are no invoices generated that have invoiced the indexation changes. If invoices have been generated, it is recommended to delete the invoice, apply the above steps and then regenerate the invoice manually.