Cannot get iPhone 6 to restore?

im trying to restore my grandmothers iPhone 6. She has locked herself out of the phone, can’t remember the password, and the phone is now disabled.

it’s telling me to connect to iTunes to erase the device. I have a MacBook which I’m trying to erase the phone through the finder. It eventually downloads the software for the phone, the phone restarts, but is still disabled. I have also tried with an older computer with actual iTunes and it still does not work.

what do I do? I hope the phone isn’t garbage now.