Hi there faizah224,
Thank you for posting to Apple Support Communities.
We understand you have a question about parental controls on your iPhone. Is that correct?
If the App Store was disabled in allowed built-in apps in Screen Time, this would explain why the app is missing. Screen Time would need to be disabled or the app would need to be allowed. See here: Use parental controls on your child's iPhone, iPad, and iPod touch - Apple Support
That should help. Let us know if you have any questions.
Take care.