Admin password lock out iMac

I was changing a couple of things on my iMac and it asked for my admin password. I put it in as I always have and it rejected it. I tried again and it rejected so I used the prior one even though I've been able to get in using my current. I was flagged with: "The password for new iMac was entered incorrectly too many times. You can approve this device using another device or reset your end to end encrypted data." Choice is to Reset or Cancel. I will not reset because of what I've read. I guess I choose Cancel. But how do I simply use my iPhone to approve my iMac? Then will I need to reset my admin password even though I haven't changed it?