Appointment
How to make an appointment for the Apple store, phone isn’t acting up bad .
iPhone 7, iOS 11
You can contact Apple Support. You can try to book an appointment at the Genius Bar or an Apple Authorised Service Provider here if they are open, but they only deal with certain issues.
Someone in the community may be able to suggest troubleshooting steps if you explain the issue you are having.
If you are able to, update your iOS version: Update your iPhone, iPad or iPod touch