F5 HA: Active F5 is gone and can't force Standby to take over

I just started working with the F5's at my company and I'm still learning my way around everything. During my process of mapping out all our existing F5's I discovered that our staging F5 was setup with HA and the B device, which was Active, doesn't exist any longer. Oddly enough it still shows as Active and the light is green next to it. I logged into the F5 Viprion host and the actual F5 Guest is completely gone. It doesn't exist on either device (Viprion A or B).

So I need to force the existing F5 that is in Standby to take over as the Active device. I know that I'm going to have to setup a new "B" and then rebuild the HA pair. But until that happens, how do I force it to be the Active device?

And as part of that question, do I need to remove it from the HA to make it a Standalone device until that is done? If so, how do I accomplish this with the least interruption?

Thanks in advance!