Update
iPhone 6s, iOS 13
iPhone 6s, iOS 13
While you seem to have already solved your tech support issue, you should know.
1: Read the warning message at the bottom of the screenshot.
2: Charge the battery and preferably leave it connected to the charge circuit during the update process.
3: Connect to a Wifi network.
4: Bonus tip. Repeatedly depleting the battery to low levels may cause premature degradation of the battery.
Update