Anyone can provide in some steps how can I manage the return from customers talking about warehouses?

My case is: 

1. I sell 100 units to my customer

2. I deliver that products to my customer from "gral" WH/location

3. My customer wants to return all the 100 products. 

4. I accept it. 

5. In my stock operation i clic on "reverse"... but now i have two quantities of the same product in the same location

After this, I see in my dashboard of my inventory and I have one movement pending from gral location to another warehouse!

Anyone can explain to me this flow

Thank you!