This module of the credit limit doesn’t have a feature where customers could pay off their credit balance. However, the upgraded version of the credit limit will come with a similar feature.

For assigning a credit limit to the customers, open the admin panel of the Magento on the Right Navbar select the customer's section, from there select the credit limit section, the credit limit panel will be opened which shows the assigned credit limit to the customers.
From there admin can see the Add New Credit Limit option and then admin can assign a credit limit to the customers.

To have a view of credit limit being assigned to the customers, from the admin panel click on the customer's section in the right navigation bar and from there select the credit limit section, a dashboard will appear which mentions all the details of the credit limit that is being assigned to the customers.

For checking the details of the credit limit from the customer's end, firstly customer has to login into his account, then he can visit My Account’s section from where he can navigate to the credit limit section which allows customers to view the credit limit section.

Yes, just like any other payment method the amount will be refunded to the customer for the returned product.

No, our credit limit doesn’t come with the partial payment feature currently.