Issue in connecting watch series 4 with iphone6

Hello ShahManish12,

Welcome to Apple Support Communities. 

We understand that your Apple Watch isn’t connected to your iPhone. We are happy to help.

Please try these steps: If your Apple Watch isn't connected or paired with your iPhone - Apple Support

"Check your Apple Watch connection

If you don't get notifications, messages, or calls on your Apple Watch, your Apple Watch and iPhone might not be connected. When your devices disconnect, the red iPhone icon  or the red X icon  appears on your watch face. You can also check your connection in Control Center. When your Apple Watch connects again, the green iPhone icon  appears.

First, bring your Apple Watch and paired iPhone close together. If you still see that the devices are disconnected and need help, try the steps below. After each step, see if your devices can connect.

Try to connect your Apple Watch and iPhone again

1. Keep your Apple Watch and paired iPhone close together to make sure that they're in range.
2. On your iPhone, make sure that Airplane Mode is off and that Wi-Fi and Bluetooth are on. To check, open Control Center. 
3. If you see the Airplane Mode icon  on your watch face, Airplane Mode is on. Open Control Center, then turn off Airplane Mode. 
4. Restart your Apple Watch and iPhone.

Unpair your devices, then pair them again

If your Apple Watch still can't connect, unpair it from your iPhone, then pair your Apple Watch and iPhone again.

Contact us

If you still need help, contact Apple Support."

These steps may help. Let us know if you have further questions.

Take care.

Hey there ShahManish12, 

What version of watchOS is currently installed on your Apple Watch? The version of watchOS you have installed will dictate the version of iOS that must be installed to be compatible.  

Have a good one!