Can't install iOS 14.2 in iPhone 7

If you are trying to update over the air, you must have wi-fi. If you cannot update via wi-fi, then you need to connect to a computer with the latest version of iTunes and update that way. See this for problems updating. If your iPhone, iPad or iPod touch won’t update - Apple Support

Read through the user tip below to see possible fixes.

Updating iOS: common issues and solutions - Apple Community

Charge the battery, and leave it attached to the charge circuit.

Connect to a WiFi network.

Attempt the update again.

What do you have connected to your Hotspot? You have to have at least 50% charge to update over wi-fi, you need to charge first.