How do I disable Guided Access on my iPhone?

• Is this an iPhone or iPad?
• Do you have a physical home button?

To do the Force Restart, which I believe you are trying, it may take a couple of attempts to get the speed and sequence of the key presses correct. For most devices:

• Press and quickly release the Volume Up
• Press and quickly release the Volume Down
• Press and HOLD the side/top button until the Apple Logo appears. This could take up to 15 seconds and you will want to ignore anything else you see on the screen during that time. If you do not see the Apple Logo, then it has not been done correctly and you will need to try again.

The support article shows this method and a Force Restart should only be needed if this does not work:

Triple-click the Side or Home button, enter your Guided Access passcode, then tap End. Or if you turned on Touch ID or Face ID for Guided Access, double-click the Side or Home button.

Use Guided Access with iPhone, iPad, and iPod touch - Apple Support

• Did you see the Apple Logo when doing the Force Restart?
• Is this an iPhone or iPad?
• Do you have a physical Home button?
• Have you tried triple clicking the Side/Home Button?
• If FaceID/TouchID was enabled when starting Guided Access, did you try double clicking the side button?

At that point it may be best to contact Apple directly as the only other options I am aware of include an unverified method of using Lost Mode, and the other is a Factory Reset that will result in data loss if your do not have an iCloud backup.

Contact Apple Support - Apple Support

• Lost Mode - If you have another device, then you can try to mark the device as lost by signing into your iCloud account. I have not verified this method, but apparently when you take it out of Lost Mode, it will no longer be in Guided Access.

Use Lost Mode in Find Devices on iCloud.com - Apple Support

• Factory Reset - This is a 2 step process that first requires erasing your device, and then restoring it from your iCloud backup. If you do not have a backup, then all data will be lost.

Restore your iPhone, iPad, or iPod touch from a backup - Apple Support