Greetings sweta2010,
It sounds like you are having issues downloading a specific app. We know how important this is for you, and we will help get you to the right place to find a resolution.
The first thing to try is the steps listed in this support article. These steps can often resolve this type of issue:
• If you can’t download or update apps on your iPhone or iPad - Apple Support
"1) Open the App Store and sign in
If a blue account button appears at the top of the App Store, you might not be signed in. Tap it and sign in with your Apple ID. Learn what to do if you forgot your password.
Learn what to do if you can't open the App Store.

2) Manually update the app
In the App Store, try to update the app manually.
3) Check your payment method
You might need to have a payment method on file, even if the app that you want to download is free. See what payment method you have on file and make sure that it isn't expired, declined, or failed.
If you can't update apps and you see a message that says “your account is disabled in the App Store,” there might be a problem with your payment method. Contact Apple Support for assistance.
4) Prioritize the download
From the Home Screen, touch and hold the app. From the menu that appears, choose Prioritize Download.

5) Restart your device
Restart your iPhone or restart your iPad.
Then check to see if you can download or update apps.
6) Contact Apple
If you still can't download or update apps on your iPhone or iPad, contact Apple Support."
Take care!