Hello, I am trying to install a fresh OS (High Sierra) in recovery on my MP 5,1 late 2009. The OS install screen says I need a firmware update first and then explains how to do this (holding the power button, the tones, etc). When I do this it restarts and it doesn’t appear to have done anything. It just tries to boot to the drive, which has a faulty OS on it (which gives me the prohibitory symbol) which is why I’m trying just install a fresh OS. How can I get this firmware update installed so I can install a new OS thru recovery? Thanks!