How can update my iPhone using WiFi

As it shows in your screenshot, you need a true WiFi connection, not a hotspot.

You also need to turn off Low Power Mode.

Connect your iPhone to a WiFi network with a strong signal and Internet access if you want to update your iPhone.

If you do not have WiFi, perhaps you have a friend with a WiFi network.

Take the phone off of Low Power Mode and keep the charger attached to the phone during the update.