We think the iPhone 6s Plus is a great phone and has retained its value.
We have found repairing the screen on this phone to be a technical challenge and certainly not something for a novice to be attempting therefore we recommend this job be done at a professional repair shop. In attempting to repair this phone we recommend doing a fair bit of research and also watch a few videos from a reputable site before starting down this road. A lot of people try to fix their own devices only to end up in our shop with a baggie full of parts.
To start, remove the screws at the bottom of the phone, you will need a special torx driver. Lift the screen off after heating it up a bit. Take your time with this and be careful not to break the flex cables. There are two sets of flex cables, one at the top, one on the side about half way down. Lift the screen up and to the right like a book. Remove the plates that hold the flex cables in place. Carefully lift the flex cables off the motherboard using a spudger. Or just pop the whole thing in a bag at this point and bring it in!!