You can add an incentive for a Friend that is an existing customer by following these steps:
1. Copy the current Live campaigns;
2. Navigate to Rules tab of the copied campaigns;
3. Scroll to the Incentives section;
4. Click on Create new incentive;
5. Select Friend incentive (existing customer);
6. Update the reward amount and attach the appropriate coupon list;
7. Launch the new campaigns;
8. Deactivate the old campaigns.