I need a help here. how do I turn ON iCloud Drive on iphone 7

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

Try a forced restart.

Reset Device

If necessary

Hard reset

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

Restore to Factory setting

Backup - Restore your device from an iCloud or iTunes backup