I have thousands of business process instance in error state

Hi Team,

I got a system to clean data and do some enhancement into it but as I was working on it, I found out that there are thousands of business process in error state I tried to cancel them but it is taking a lot of time

Please suggest a way to cancel them.

there are thousands of records and easier way to delete them currently 

I wish to use SQL Execuer to delete data so please let me know if I am correct and its impact on the system and correct usage

Thank You in Advance