If I understand what you are trying to do, you have midi data on a midi track, and you want to use Session Drummer 3 to play that midi data.
You need to connect the dots between SD3, a midi track, and one or more audio tracks, to be able to hear/record drums with SD3.
Given that you already have the midi data on a midi track, once you have SD3 loaded with the desired kit in the synth rack, you will need to (this is just a simple example):
1. Insert a stereo track for the drum sounds to be heard.
2. Set the Input for the audio track for drums to the stereo output from SD3.
3. Set the Output for the midi track with the drum data to SD3.
4. Hit Play
Give the above a try and post back,
Bob Bone