The REGI.EXE tool is located in your OS file system. The location is visible from the HANA Studio by going to Windows > Preferences > SAP HANA Development > Repository Access. For example:
C:\Program Files\SAP\hdbclient\regi.exe
As I too have the a similar error as yours I am trying to learn how to use this tool in order to resolve a conflict.
Best regards,
Jeff Holdeman
SAP Labs, LLC / Customer Solution Adoption (CSA)