Although it may look frightening, but in fact, this is quite easy, you just have to play the same notes but with every flat there is on the keyboard. Only instead of F sharp play F natural.
Here is the PDF score and a MIDI file for listening. Play it 3 times in a row correctly. After you are done practicing, post your time to comments.
These few transposition exercises serve as an introduction to my Transposition for Organists Level 1 course which I'm preparing to release so if this kind of training would be helpful to you, be on the lookout for an official anouncement from me soon.