On an iPhone 12, hold the side button together with either volume button until the power-off slider appears. Move the slider and allow about 30 seconds for shutdown. To start the phone again, hold the side button until the Apple logo appears. These are Apple’s normal restart instructions.
Locking is different from shutting down
A short press of the side button normally locks the display. The phone remains running, so calls and background activity can continue. Use the power-off slider when your intention is to shut the phone down.
If you are preparing for support, note the problem before restarting: the application involved, the error, and when it occurred. This helps distinguish a one-time interruption from a recurring issue.
If the phone is unresponsive
A frozen screen may prevent normal shutdown. Apple links separate force-restart guidance from its restart page. Follow the instructions for your exact model; do not treat a factory reset or data erase as the next ordinary troubleshooting step.
Before a repair handoff
Confirm the state of your backup and explain what information must be retained. For a business-managed phone, coordinate with the person responsible for its accounts and device management. Avoid sending account passwords in an ordinary support message.
Check the original problem afterward
Once the phone restarts, repeat the task that failed. Record whether the issue returns and whether it affects one application or the whole device. If you need assistance, contact Your Expert Tech with the model and symptoms rather than only saying the phone needs a restart.