Here's How to Customise Action Button on Your iPhone
To start customising, begin by opening the Settings app on your iPhone.
Representation of home screen template for smartphone.

Customising the Action button on your iPhone allows you to tailor the device to better suit your needs and preferences.
Here’s a simple guide on how to set it up:
Access the Settings Menu: Begin by opening the Settings app on your iPhone.
Find the Action Button Settings: Select "Action Button" from the list.
Choose Your Action: Swipe left or right to browse and select the action you want to assign to the Action button.
Save Your Selection: Tap the Back icon, then hit "Save" in the upper-left corner to confirm your choice.
Alternatively, you can configure the Action button through Accessibility:
Open Accessibility Settings: Go to Settings, scroll down, and tap on "Accessibility."
Navigate to Action Button: Under "Physical and Motor," select "Action Button."
Set Your Preferred Action: Choose the action you’d like to assign.
Common actions for the Action button include toggling Silent mode, activating Focus, opening the Camera, or turning on the flashlight.