you might want to tell Amazon who can make those changes by emailing them at email@example.com instead of asking the powerless members of this customer to customer help forum. We can't do anything
I fixed this issue on my device. I discovered that in All Settings -> Language & Dictionaries -> Language, I had selected "English (United Kingdom)" when I set up my Paperwhite for the first time. I changed this to "English (United States)" and the time settings now show a 12-hour clock time with AM and PM. I realized what I had done from the spelling of words in a dictionary lookup.