Q: can i replace my iPhone 6 if my wifi chip doesn't work ?

Natalia, if the chip is not working properly Apple can replace your phone. The cost depends on warranty status. Check this article for details. Good luck.

https://www.apple.com/support/iphone/repair/other/

Possibly if the iPhone is still under warranty.

Check your support coverage here >  https://checkcoverage.apple.com

Find the serial number of your Apple hardware product

Otherwise, try the troubleshooting steps here >  If your iPhone, iPad, or iPod touch won’t connect to a Wi-Fi network

Take it into an Apple Store or Authorized service provider and have them diagnose it. If the Wifi failure is determined to be a manufacturing issue and as such is covered by warranty they will very likely replace it.

If it is found to be user caused, or by tampering with the iPhone, then probably not.