Greetings aishwarya251,
Thanks for visiting the Apple Support Communities! I understand you're unable to transfer the data from your previous iPhone to your new iPhone using Quick Start.
The following article provides helpful steps for transferring data with Quick Start: Use Quick Start to transfer data to a new iPhone, iPad, or iPod touch - Apple Support
If you're using the wireless method to transfer data with Quick Start, then I suggest ensuring you're using a fast and reliable network. If you're using the wired method, then I suggest ensuring you're using a 12W or higher power adapter, as outlined in the following section:
"You might choose the wired method if the wireless network that you're using is slow or congested.
If you want to migrate your data wirelessly, keep your previous iPhone near your new one throughout the process as you follow the steps below. Make sure to keep both devices connected to power.
To migrate data using a wired connection, get a Lightning to USB 3 Camera Adapter and a Lightning to USB Cable, then follow these steps:
- Connect the Lightning to USB 3 Camera Adapter to power through its Lightning port. Make sure to use a 12W or higher power adapter.
- Connect the Lightning to USB 3 Camera Adapter to your current iPhone.
- Plug the Lightning to USB Cable into your new iPhone, then connect the other end to the adapter.
- Continue by following the steps below."
If data migration continues to fail with Quick Start, you can also transfer your data from a backup created by your computer or iCloud: Transfer data from your previous iOS device to your new iPhone, iPad, or iPod touch - Apple Support
Kind regards.