My ipad is not updating after being connected to wifi from my iphone

For your iPad to install an available update, its battery must be charged to at least 50% capacity - and/or be connected to its Power Adapter. Similarly, the iPad can only be updated over a standard WiFi connection - not a Cellular hotspot - or be updated by a PC or Mac using iTunes or Finder over a USB connection.

The iPad will not update when using a Personal Hotspot, since that is cellular. You need to be connected to an actual wi-fi network to be able to update the iPadOS.