How can I get into my iPhone 7 Plus when it is disabled without iTunes

You cannot. Once disabled you need iTunes on a computer to restore it.

If you can borrow one from a friend or family, or go to an Apple Store, and ask to use one of the floor models.

See the following from If you forgot the passcode for your iPhone, iPad, or iPod touch, or your device is disabled - Apple Support

If you don't have iTunes, download and install iTunes on your Mac or PC. If you don't have a computer, borrow one from a friend, or go to an Apple Retail Store or Apple Authorized Service Provider.