Via Customer Journey AND Rewards Store
1. Log in to your BetMGM account and access your profile on the top right corner
2. Select Account Details > My Rewards > Marriott Bonvoy Rewards > Link Account
3. Sign in as usual to Marriott Bonvoy
When you see a message confirming your Marriott Bonvoy account has been linked, select Convert Points in the Rewards Store or Unlink Account.