To redeem a Roblox gift card worth, please follow these steps:

Visit Roblox.com/redeem from your browser.
Log in to your account or create a new one.
Find the PIN code on the back of your physical gift card or in your email if its a digital gift.
Enter the PIN code in the white box on the website.
Click on the Redeem button.
Please note that Roblox gift cards can only be redeemed in a browser at Roblox.com/redeem and not in the Roblox mobile app or any video game console. Also, you can only redeem gift cards that are for the same currency as the country where your Roblox account is registered. For example, if your Roblox account country is set to the United States, you can only redeem gift cards in US dollars.