You should receive the letter to renew your licence about 2 months before the expiry of your licence.  The letter will provide you with an acknowledgement number which you must enter in your application form via GoBusiness portal

Upon approval of the renewal application and payment of the prescribed fees, the Police Licensing and Regulatory Department will send the licence you a letter by post to inform you that your licence has been approved.

You may refer here.

This information is sourced from SPF-STAGING