Your backup is a .dmg file (disk image) double click the file to mount it (open it) once mounted you’ll see the company file, drag that to documents>quickbooks, now use file>open company and navigate to the file.

Resolution for 'corrupted issue: 'Quickbook for Mac file corrupted. How do I restore from backup? No option to restore from backup.' available: Yes.

The corrupted issue or error code is a known issue in Quickbooks Online (QBO) and/or Quickbooks. Support for this issue is available either by self-service or paid support options. Experts are available to resolve your Quickbooks issue to ensure minimal downtime and continue running your business. First try to resolve the corrupted issue yourself by looking for a resolution described in the article. If it is a complex corrupted issue or you are unable to solve the issue, you may contact us by clicking here or by using other corrupted support options.

For more information about resolving issues related to corrupted in Quickbooks/QBO or to get support for the issue 'Quickbook for Mac file corrupted. How do I restore from backup? No option to restore from backup.', click the link below: