Find the game in the list and click "Report a Problem". This will expand the row, revealing a form:
If you're requesting a refund because, upon opening the game, you're seeing a message informing you that your device isn't compatible, choose "Problem is not listed here" and in the description box write:
"I would like to request a refund because this application isn't compatible with my device."
Otherwise, select the option that most closely matches the issue you're having.