You must create a classic email template to notify reviewers when a review cycle is cancelled.

To create the parallel review cycle cancellation email template

  1. Go to Setup > Email > Classic Email Templates > New.
  2. Select HTML and click Next.
  3. Enter ParallelReviewCycleCancelNotification in the Email Template Name field.
  4. Select remaining options according to your requirement and click Next
    For more information, see Salesforce documentation.
  5. Add a subject for the message and add an HTML message.
  6. Click Next.
  7. Click Copy text from the HTML version to automatically paste the text from your HTML version without the HTML tags.
  8. Click Save.