How to add an automated counter field in Zoho CRM
You can create an auto number field by following these steps:
- Log in to Zoho CRM with Administrator privileges.
 - Click Setup > Customization > Modules and Fields.
 - Select the Module from the Modules list view.
 - Drag and drop the Auto Number field type from the New Fields tray.
 - In the Auto Number Properties popup, do the following
 
- Enter a name in the Field Label field.
 - Under the Auto Number Format section, enter the Prefix, Starting Number & the Suffix for the auto number value. Check the preview.
 
      6.  Click Done.
      7.  Click Save Layout.

Also see an example in the attached video.