If your Gopay registration process has been declared successful, you will receive an Email from Midtrans for the registration process to the Midtrans Portal. Midtrans Portal is a portal from Gopay to view your account details (such as transactions, payments to accounts).
Midtrans Portal Registration
Step 1. Open your Email Inbox
You will receive a registration Email to enter the Midtrans Portal. Click "Click here to login" button

Step 2. Fill in the Registration Form
Enter the required data for your Midtrans account

Step 3. Login in the Midtrans Portal
Enter your registered Email and Password

Step 4. Login Successful
After successfully logging in, you will be directed to the Dashboard page

You might also like to read this article:
Has your registration been successful? You need to first input the server key into DealPOS so that the registered QRIS can be used by the cashier. For details, check the following article: Input Server Key Gopay QRIS in DealPOS.
To change the merchant name, you can check the following article: Changing your Merchant Name.
FAQ about using midtrans, you can check this article: FAQ (MDR + Payout).