Hello asmintha,
Just to clarify, does anything appear on the screen of your device, or is it completely blank? If the device isn't responding, please check out this link, which has some suggestions that may help with that issue: If your iPhone won't turn on or is frozen
If your screen is black or frozen
Follow the steps for your device.
On your iPhone 8 or later, including iPhone SE (2nd and 3rd generation)
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.
If that doesn't help, please contact Apple Support for assistance. You may be able to reach them here: Get Support
Thanks!