Hi SunnyInToronto,
We can't reinstall an update. However, you can do a restore using your computer. This will remove everything on your iPhone, and reinstall the iOS software. You can then reinstall your backup, either computer or iCloud.
If the issue returns, then you'll need to restore again, and set up as new.
Restore your iPhone, iPad, or iPod to factory settings - Apple Support
Restore your iPhone, iPad, or iPod touch from a backup - Apple Support
You also asked about using iCloud for your backup. You most definitely can, as iCloud security will protect your personal data.
iCloud data security overview - Apple Support
What does iCloud back up? - Apple Support
Take care!