Phone locked in guided access mode, password forgotten and forced restart not working
if phone is in guided access and you turned on Touch ID or Face ID for Guided Access:
you can end a session with a double-click on the Side or Home button.
Else: Forced restart generally works in this situation, so you may want to double-check the method:
Force restart iPhone - Apple Support & there are trouble-shooting tips at the bottom of the article
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If you still need help:
There's a discussion thread (link below) where a community member shares what they did in a similar situation. NB: Am no expert, and have no way of checking this solution out, so do not know how reliable that method may be. Phone is stuck in guided access and can’t… - Apple Community
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If needed:
For assistance from Apple's Accessibility Support Team:
See: How to contact Apple for help with accessibility features - Apple Support