There is no factory reset for this device. But there is a procedure that is the equivalent.
Unfortunately for you, at least until the next guy comes along, I no longer own a rack unit, and haven't reset my floor units in quite some time for me to know how to do it without Monkey.
PLUS, how does this work with the Model Packs. All this, I don't know.
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Ultimately, all that to say I can't help you - other than to tell you there is no one click factory reset.
But I am glad you brought it up, because I am sure someone (me) is going to need to know this at some point.
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And replaced with Line 6 Central.