Cannot connect to the AppStore

Do you have access to another WiFi network where you can try? That has worked for several people.

Try a restart.

Restart your iPhone, iPad, or iPod touch https://support.apple.com/en-us/HT201559

Try a forced restart.

Reset Device. https://support.apple.com/en-us/HT201412

If necessary

Hard reset. https://www.wikihow.com/Hard-Reset-an-iPhone

Do a backup and try a factory reset. Then restore from your backup.

Restore to Factory setting. https://support.apple.com/en-us/HT201252

Backup - Restore your device from an iCloud or iTunes backup. https://support.apple.com/en-us/HT204184

Device or computer? Do you have access to another WiFi where you can try again?