Q: Hi everyone! My wifi toggle switch is greyed out on iphone 6

There's a few things you can do if your wi-fi button/switch is grayed out.

1, Restart the device

2, Check for any iOS updates

3, reset network settings Settings>General>Reset> Reset all network settings

4, last and final step is to restore the device via itunes or through Settings>General>Reset>reset all settings and content
***Make sure you've done a backup before this step***

There are a couple of suggestions in both of these articles.

If Wi-Fi is grayed out or dim on your iPhone, iPad, or iPod touch - Apple Support

http://www.imore.com/if-wi-fi-option-grayed-out-your-iphone-or-ipad-heres-how-fi x-it

You may have to restore the iPhone as a last resort and if that still fails to fix it, you will need to contact Apple Support or bring the phone into an Apple Store for help.