Help with doing a factory image

I my tablet has been super slow since the Marshmallow update. Often the screen doesn't recognize any touches. YouTube skips and is laggy, as well as every app. I have a the KitKat factory image downloaded and unzipped but I'm kind of stuck. 2 years ago the usb port on it broke. Since then the only way to do a backup or get things on it is by email or something like Dropbox. For charging I use the wireless charger that came with my phone. But now I don't know how I'm going to be able to do the factory image install without plugging it into my computer. The USB port is dead. I'd really like to have use of my tablet again but I'm not sure what I can do. There might be a small chance I can get the usb to work but that's a 1/1000000 thing... Help?