Keyboard lagging

Hello Prashant0603,

Welcome to Apple Support Communities. 

Please use the steps here to restart your iPhone as listed here: Restart your iPhone - Apple Support

1. Press and hold either volume button and the side button until the power-off slider appears.
2. Drag the slider, then wait 30 seconds for your device to turn off. If your device is frozen or unresponsive, force restart your device.
3. To turn your device back on, press and hold the side button (on the right side of your iPhone) until you see the Apple logo.

We also recommend the steps in the section titled “If your screen is black or frozen” here: If your iPhone won't turn on or is frozen - Apple Support

1. Press and quickly release the volume up button.
2. Press and quickly release the volume down button.
3. Press and hold the side button until you see the Apple logo.
4. If your phone doesn't turn on, follow these steps to check your hardware and charge your phone. You might need to charge for up to an hour.
5. If your phone still doesn't turn on, contact Apple Support.

Let us know if you have further questions.

Take care.