If you need to create an order manually, then you can create a draft order in your Shopify admin. For example, if your customer didn't receive your product and you want to send a replacement product, then you can create a draft order. Learn more about creating draft orders.
Steps:
From your Shopify admin, click Orders.
Click Create order.
Click Browse, select products to add to your order, and then click Add.
In the Find or create a customer section, add a customer.
Optional: In the Notes section, add an internal note that you're sending a replacement product.
Click Mark as paid to discount your order by 100%.
Click Create order.
After you create a draft order, then it shows up in Oberlo and you can place your order.