How can I reset my forgotten restriction passcode in my iPhone 7?

Use Restrictions on your iPhone, iPad, and iPod touch = About Restrictions (parental controls) on iPhone, iPad, and iPod touch - https://support.apple.com/HT201304 - including what to do if you forgot the code (see also: https://discussions.apple.com/thread/7846481?answerId=31330560022#31330560022)

The restrictions passcode cannot be bypassed. However, no harm comes from guessing the passcode.

Here are your options:

1) You can erase the phone and start over fresh, but you will lose all of your content and settings.

2) You can live with the restrictions and hope that someday you remember the passcode.

Be aware, the restrictions passcode is quite different from the phone's unlock passcode...that puppy will disable your phone if you try to guess it too many times.