Microsoft, Sony, and Steam accounts can be linked or unlinked by visiting the profile section of the Call of Duty site.

Note: Unlinking and relinking accounts can cause corruption with Season Pass, DLC, Micro DLC items, or other entitlements applied to your accounts. Please avoid any unnecessary unlinking and relinking of accounts.
  1. Click the gear icon and select Profile.

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  2. Scroll down to the Consoles section to link or unlink a console. To link, select a console you wish to link. To unlink, select a linked console.

    User-added image
When linking an account, you will be temporarily taken to the console manufacturer's website to confirm your credentials. Once confirmed, your console will be linked to your Call of Duty account.