Printer Repair Questions? Ask IT Technicians for Answers ASAP
I don't know what means of starting the scan you are using, but the prompt for 'Computer' means, basically:
"What destination machine on the network do you assign as the storage location for this scan operation?"
So yes, Myrnna's MAC, if that's the name, on the network, of your computer, is the right thing to enter... even if you have to type that in.
If there's trouble, make sure your iMac is, actually, connected before even starting the scan. (And double-check, perhaps, that the iMac is still named 'Myrnna's MAC'.)