I can’t download software update downloading not start how I do

Go to Settings/General/About and look at Modem Firmware. Is the entry blank? If it is you need to reinstall it by restoring the phone to factory settings, then restoring a backup. Back up the phone first, of course:

1. How to back up your iPhone, iPad, and iPod touch - Apple Support
2. Restore your iPhone, iPad, or iPod to factory settings - Apple Support - follow the instructions to restore using your computer, do not using Settings/General/Reset (which is not included in those instructions)
3. Restore your iPhone, iPad, or iPod touch from a backup - Apple Support

If the modem firmware DOES have a value you may have a hardware problem. The first step is what I just posted, but after that you need to contact Apple support using the Get Support link at the top of this page.

You are are using a hotspot for internet. You need a direct Wifi connection, NOT from hotspot. And you should also plug your phone in to charge as you're at 53% battery and you'll need the battery to remain above 50% to be able to update.

my phone bill is paid and I’m connected to WiFi idk what to do

You will also need a SIM in the phone to activate it during the update.

oops, I missed that little tidbit.