To disable the approval emails - go to Setup > Workflow Rules

  1. Deactivate "Send Account Owner After Client Submit Form" rule, if you're sending forms from Account Record. 

  2. Deactivate "Notify Contact Owner when Contact Submitted UpdatedForm" rule, if you're sending forms from Contact Record.

  3. Deactivate "Send Lead Owner After Client Submit Form" rule, if you're sending forms from Lead Record.

Click the Save button.