Unfortunately, there's no direct way to retrieve your CET register number using your Aadhaar number. The register number is typically assigned by the specific CET (Common Entrance Test) conducting authority and is linked to your application form and other personal details.

However, here are some options you might consider:

1. Contact the CET Conducting Authority: Reach out to the organization that conducted the CET in 2019. They might have a process or helpline to assist you in retrieving your register number, especially if you can provide additional details like your name, date of birth, or other information from your application.
2. Check Your Previous Application or Admit Card: If you still have a copy of your CET application form or admit card from 2019, the register number should be printed on it.
3. Search Through Your Documents: Look through your old documents, emails, or folders for any correspondence related to the CET that might contain your register number.
4. Contact Your Educational Institution: If you were applying to colleges through CET, your educational institution might have a record of your register number.

Remember to provide as much information as possible when contacting the CET authority or your educational institution to increase your chances of retrieving the number successfully.

I hope it helps !!