How to design the solution to process large population of records in CRM

Hello Experts,

Hope you all are doing well.

Here looking for a best solution to address one business need. Business want to send SMSs  to customer's to participate in the Poll.

In CRM we have a custom entity to control SMS content, URL and reminder and an external database to manage the transactions.

From CRM side I need to process all records and update the SMS content and Shorten the URL and update the same to an external database. To shorten the url using 3rd party api.

My ask is how to design the solution which can process millions of records without any issue, currently thinking to develop a console app to handle all this requirement.

How to avoid performance issue, If I put this much population in a foreach loop/parallel foreach loop  to process the records and perform update on CRM entity record, calling 3rd party api to get shorten url in response & updating in CRM entity and updating external database.

Appreciate your help to design a best solution.

Thanks.