I haven't used this type of LCD, but have just had a look at the data sheet and sample code available here;
http://www.crystalfontz.com/products/document/2373/CFA635-TMF-KU_Data_Sheet_v2.1.pdf[
^]
Think it is a pretty standard setup, read the button pressed, write the display you want to show, and repeat.....
Have you visited the OEM website and see if there is any more info on there.
You could also asked mroe specific questions and search their tech forums;
https://forum.crystalfontz.com/[
^]