It's possible to install a Greek keyboard on a desktop computer as well; https://www.duolingo.com/comment/17706271 has some links.
That doesn't change your keycaps, but the layout is similar enough for most letters that you can either get used to it fairly quickly, or you can mod your keyboard with a marker or stickers to add the Greek letters as a reminder.
You can check out this discussion here https://www.duolingo.com/comment/17706271
(Please make sure to always check the Discussion section of the course. This is a topic we get a lot of reports for, although there is almost a gazillion of comments and discussions that include all the links. ^.^)
Happy learning! ^.^
This Forum is for language-related discussions. Technical problems are out of our jurisdiction.
This sounds like something to notify Duolingo staff of directly and you would be helping a lot if you reported here: