How to unlink your Epic Games Account:

Step 1:,
Open the following link:
Rockstar Support

Step 2:,
Scroll down until you see the "Submit a Ticket" section. (See reference image.),

Step 3:,
In your Rockstar ticket, write that you would like to unlink your Epic Games account. Be sure to include the following information:
Epic Games ID,
Epic Games Username,
Rockstar Games Username,

How to Find Your Epic Games ID:,
Open the Epic Games Launcher.,
Click your account name at the bottom left corner of the screen.,
Select "Manage Account" from the left sidebar. This will open a new browser window.,
Navigate to "General" in the left sidebar.,
Your Epic Games ID will be displayed at the top of the "Account Info" section.,

Step 4:,
Take a screenshot of your Epic Games ID and attach it to your ticket using the Upload File button.