Welcome to the community!
Are you sure it's 5GB or 5 hours? If it's the 5hrs then you can access it through the Fido My Account app.
If you did get an offer for an extra 5GB of data the message should tell you how to claim it. Most time you can log in to your account and accept the offer or it should be available in the Fido app also.
If you do not see any way to accept the offer then you can contact customer service directly and they will be able to assist you with adding the offer to the account.