forget passcode of Guided Access

Life hack: sign into your icloud, “find my iPhone” from any computer and put your phone into lost mode. That will take your phone out of “Guided Access” and take you to your main Lock Screen. Enter your normal password then I’d recommend resetting your guided access from your setting menu. Hope this helps.

1. Force restart the iPhone / iPad --> Force restart iPhone - Apple Support
2. iPhone restarts> Enter Lock Screen Passcode --> Click-> If you forgot the Lock Screen Passcode for your iPhone, iPad, or iPod touch, or your ...
3. Then go to Settings -> Accessibility -> Guided Access and change the passcode