OSS Endpoint - How to install older firmware

A bug in 6737i requires I change the firmware.

How do I install different firmware for my Aastra 6737i phones so that OSS Endpoint Mgr will download it?

Or, should I remove the device from the OSS Configuration and just update the phone?

Just delete the old model.st file in tftpboot and copy the one you need.

Thanks, where is tftboot located?