I tried many time to setup Hey Siri but it is always show "Siri didn't quite get that. Try again"

Hi iamabhaygupta,

We'd be happy to help with getting Hey Siri set up with you today.

Start by temporarily disabling Bluetooth from Settings > Bluetooth. That'll help with ensuring that there aren't any accessories, such as headphones/speakers/etc. that may be interfering.

We'd then suggest checking out the steps here, which can help out with microphone-related issues: If the microphones on your iPhone aren't working

If you find the audio quality is poor in the test recordings made via the Camera app and/or Voice Memos, then you'll want to explore your available servicing options. You can contact Apple Support here directly to do so: Get Support

If the audio quality was fine in the Camera app recording, and in Voice Memos, then the next step would be to restore the device to factory settings using a computer, and try again: Restore your iPhone, iPad, or iPod to factory settings

As this will erase the device, be sure to back up ahead of time: How to back up your iPhone, iPad, and iPod touch

Take care!