Using iPhone 6s+ for boost from sprint?

I have an iPhone 6s+ with Sprint that I've paid off and don't use anymore. My sister uses Boost mobile and so I'm wanting to give her my phone. I just found out that phone isn't currently eligible to work with Boost from Sprint. How would I go about unlocking my phone so that she's able to use it?

I replaced the screen to my iphone 5 but blue vertical lines appear and the touch is not working

I reassemble the screen after seeing some youtube videos tryed to brush connectors with a shoft toothbrush… And now when i opened the phone it turned up alright but after seconds the lines apeared again and now half top of screen does not recognise touch,

i have made may replacments but first time i encounter a problem.
so could it be that my connectors are fried or something? Is this something that can be fixed?

How to make computer (Windows) keyboard act more like iphone keyboard?

Academicy type person here - have to frequently type words or names from other languages with different lettering (or accent marks), and was wondering if there are any programs out there to get the computer keyboard to act more like the iphone - where instead of holding down repeats the letter, options pop up for different lettering.

Can you transfer apps from one iPhone to another?

I have a music app on my current iPhone and i was wondering if i can transfer it from this phone to my new phone. The app isn't available for download anymore btw that's why i'm asking if it's possible to transfer it.