Q: iOS9 update defect

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Recommended settings for Wi-Fi routers and access points - Apple Support

If you did and to rule out a software problem, try to set it back to factory settings, without using any backup data afterwards and test the Wi-Fi network function.

Use iTunes to restore your iOS device to factory settings - Apple Support

If still an issue, get the phone checked by Apple or an Apple Authorized Service Provider next to your place.

Start a service request

Find an Apple Authorized Service Provider

Make an Apple Store appointment