firmware failure when downgrading, router out of service

We have two routerboard433 v.4.5 in a link, and, tried to downgrade remotely via wirelessly one of them, but, the remote radio could not downgrade succesfully, so it is out of service. We used the COM port together with ehter1 port to re-install routerOS but did not work. What else can we do to recover this radio. Any helpe is appreciated :smiley: