How to set up a annual subscription email function in a campaign


We have a subscription which contacts subscribe to for a minimum of 12months. Each contact could sign up at different times so the start date / renewal date will all be different. After the initial 12month period the subscription is ongoing until they cancel. We manage this through custom tags specifically the start date and renewal date.
Every 12months on their anniversary we send them an email (through the campaign) reminding the contact another year has passed and if they would like to make changes etc.

We are trying to set up the sequence where after the first 12months has passed, the contact’s “renewal date” is updated/overridden to the next year’s date i.e. 20th April 2022 is changed to 20th April 2023.
Then the contact is looped back into the front of the sequence where we wait until 30days before their “renewal date” and send them their annual reminder.

Can anyone please let me know the best way to do this?

Keap does not have the functionality to override the custom fields with a dynamic date, so we are looking for other options that can achieve our goal.

Thanks you in advance.