Redeeming your Overwatch Coins is quick and easy:On Xbox:
Press the Xbox button to open the guide and select Store
Press the View button to open the side menu and select Redeem
Enter your code, select Next, and follow the prompts on your screen
On PC (Battle.net)
Open the Battle.net App
From the BattleTag, click the drop-down and select the Redeem a Code button found above the Log out button
Enter your code and select Redeem Code
Head over to the Battle.net Shop and find your preferred Overwatch Coins
Pay with your newly acquired Blizzard credit