Hi gauravdada92,
We understand that your notification sounds aren't as loud as you'd like them to be.
You can adjust the volume of your notifications by using the side buttons on your iPhone or in Settings > Sounds & Haptics. You can learn more here: If you hear no sound or distorted sound from your iPhone, iPad, or iPod touch speaker - Apple Support
If the sound isn't working on your iPhone, the troubleshooting steps outlined here may help you: If you hear no sound or distorted sound from your iPhone, iPad, or iPod touch speaker
Follow these steps
1. If your device has a Ring/Silent switch, move the switch forward—toward the device's display—so that orange isn't showing. If you're using an iPad, you can also swipe down from the top-right corner to open Control Center and make sure that Silent Mode is off.

2. Open Settings > Focus > Do Not Disturb and make sure that Do Not Disturb is off.
We hope this helps.
Cheers!