Dear Deepnaruka,
You may apply through online portal of HEPCB at least 90 days prior to the date of expiry of previous CTE in the prescribed proforma along with declaration and undertaking as per Annexure-VIII along with prescribed CTE/NOC fee and documents.
Don't get confused. After login you can arrange required documents accordingly. If there would be any problem then you can directly contact/visit to HEPC office.