my iphone7 will not "activate" in the finder window when i try to reset/update it

Connect iPhone to Mac

Use your USB lightening cable --> Resolve USB-related alerts in iTunes - Apple Support

If unable to connect --> If iTunes/Finder doesn't recognize your iPhone, iPad, or iPod - Apple Support

For your Mac --> If your computer doesn't recognize your iPhone, iPad, or iPod ...

Use genuine cable --> Identify counterfeit or uncertified Lightning connector accessories ...

See how to --> Sync your iPhone, iPad, or iPod using iTunes on your computer ...

If you are experiencing an issue not listed here, contact support

Power off the phone

Shut down the Mac

Connect the Lightning cable from the phone to the USB port on your Mac

Restart the Mac

Power up the iPhone

Open any Finder window on the Mac and look on the left panel under Locations....or it might read Devices

If things are working, you may be asked to "authorize" the Mac as a connection source.