i can’t use wifi to upgrade my software. can i use enough data to upgrade my software ?

On an iPhone 6S, no you need to use WiFi or a computer.

Update your iPhone, iPad, or iPod touch

• If you have an iPhone 5S or 6/6plus, the highest you can update to is 12.5.5

• If you have an iPhone 6S through 13, you can update to 15.5

Go to Settings > General > Software Update.

Update your iPhone, iPad, or iPod touch using WiFi -

Update your iPhone, iPad, or iPod touch - Apple Support

Update using your computer -

Update iOS on iPhone - Apple Support

You cannot use cellular data to update your phone, you can only use Wi-Fi. If the Wi-Fi switch is grayed out your phone has suffered a hardware failure; it probably isn’t worth the investment to repair a 7 year old phone.

I can’t put on my wifi

But is there a way to solve this problem am using an iPhone 7pluse

There is no way to solve the problem if Wi-Fi is not working.