In order to configure Magento 2 Guest to Customer Extension:

1. Navigate to Stores > Configuration > Magefan Extensions > Convert Guest to Customer.

Magento 2 Convert Guest to Customer Configuration

2. Enable or disable the extension.

3. Enter the Product Key which is found in your Magefan Account > My Downloads.

4. Enable the Automatic Conversion of Guest orders to Customers in case there a lot of guest orders placed on your store every day and you want the customer accounts to be created instantly after the placement.

5. Choose whether to assign an Order Address to Customer or not.

6. Choose whether you want to Send  Welcome Email. If you set this option to Yes, the email will be sent to the user once the guest order is converted to a customer.

7. There is also an option to Convert All Old Guests To Customers in case you've just started using this extension and have plenty of guest orders you would like to convert at once.

Magento 2 convert guest to customer

Once you've finished with all the configurations don't forget to press the Save Config button.

Magento 2 Convert Guest to Customer Extension Save Config