Downgrade from 19.2 to 12.3

Hi,

I recently upgraded a cluster of SRX5400 from 12.3 to 19.2 and I need to revert it back to 12.3. When I try I get the error:

ERROR "/usr/libexec/ui/downgrade" the bootstrap installer is missing...

Is it possible to downgrade this directly from 19.2 to 12.3? Note that access to the cluster is remote so I can't use the USB method.