You may need to be signed in to your Apple ID on your device before you can use the App Store:
Sign in with your Apple ID - Apple Support
And
As you have recently changed yourApple ID password:
What to do after you change your Apple ID or password - Apple Support.
You may need a payment method listed in your Apple ID account for the first time you use the App Store, even if you are downloading free apps.:
Change, add, or remove Apple ID payment methods - Apple Support
How to: Get apps in the App Store on iPhone – Apple Support
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Else:
Troubleshooting:
If you can't open the App Store or iTunes Store, buy content, or edit payment information - Apple Support
If you can’t download or update apps on your iPhone or iPad – Apple Support
If help is still needed:
You might want to reach out to the App Store Support Team:
(There is a "Get Support" link (or use the support app) at the bottom of their webpage (link below)
App Store - Official Apple Support