In order to configure Login as Customer Extention please go to Admin Panel > Stores > Configuration > Magefan Extensions > Login As Customer.
Login As Customer Information
1. If you want the page cache to be disabled for you as a customer, choose correspondingly Yes in the Disable Page Cache for Admin User field.
2. If choose Yes in Keep Guest Shopping Cart Items guest shopping cart will be merged into customer shopping cart during the login process.
If all configurations have been performed don't forget to press the Save Config button.