Hello Handian Sudianto,
Welcome to the Microsoft Q&A and thank you for posting your questions here.
Regarding your question to decrease Elastic Pool Storage, after the storage went back to normal do you clean up the database?
I will advise that you should remove unnecessary data, I mean some of your old logs, temporary data, or unused tables and it's better if you can archive old data to another storage solution if necessary and it is not frequently accessed. Then, if reducing storage is not feasible, consider other options such as splitting the databases into multiple elastic pools or using different Azure SQL Database tiers.
I hope this is helpful! Do not hesitate to let me know if you have any other questions.
Please don't forget to close up the thread here by upvoting and accept it as an answer if it is helpful