If you have customer data and also act as a supplier of your products. You no longer need to create or add supplier data manually. You just need to follow a few simple steps as follows:
Step 1. Go To Menu Contact
click on one of the customer names that you want to make as a supplier too

Step 2. Click the Down Arrow Button on the Contact Details Page, Then Click "Create Supplier From This Customer"

Step 3. Create Supplier From Customer Contact Successfully

You can try to make sure again in the contact supplier data :

You might also like to read these articles below:
To add new sales person, you can check this article Add New Sales Person
If you want to create a customer group for multiple customers, you can check this article Create Customer Group
If you want to add customers/suppliers in bulk, maybe you can check the steps in this article Import Customer / Supplier
To add member exclusive for outlet, you can also check this article Member Exclusive for Outlet