My iPhone WiFi doesn’t work how can I on it?

Open Settings. Look at Wi-Fi and Bluetooth.

Is the switch off for both? Can you turn either one on? If you cannot turn either on, your radio chip has failed; this is a hardware problem. You can try backing up the phone, then restoring a backup, but if that doesn’t resolve the problem it is time for a new phone; investing in the repair of an obsolescent device is generally not cost-effective.