Hi,
To continue using free services for remainder of 12 months since you signed up you need to upgrade to Pay-As-You-Go account:
Upgrade your Azure free account or Azure for Students Starter account
https://learn.microsoft.com/en-us/azure/cost-management-billing/manage/upgrade-azure-subscription
As long as you only use the free services and stay within the limitations, you will avoid charges. Please review article below:
Avoid charges with your Azure free account
https://learn.microsoft.com/en-us/azure/cost-management-billing/manage/avoid-charges-free-account
Please click Accept Answer and upvote if the above was helpful.
Thanks.
-TP