Hi Xu Chen, great to hear from you.
If you are not on a paid plan, then the retention is set permanently to 60 days. If you are on a paid plan, then new tables should get created with the new TTL. You can create commands to do this for pre-existing tables with a query like the following:
SELECT CONCAT("ALTER TABLE `<PROJECT_ID>.analytics_<PROPERTY_NUM>.", table_id, "` SET OPTIONS (expiration_timestamp=NULL);") AS cmd
FROM `<PROJECT_ID>.analytics_<PROPERTY_NUM>.__TABLES_SUMMARY__`
WHERE table_id LIKE 'events_2020%'
☼, Kato