Here’s a quick video explaining how to develop your fill playing for Train beats. The key thing is to drill a bunch of accent patterns (and ideally memorise them) at a slow tempo and in relaxed style. Once you can play them, add each one to a bar and a half of Train beat and play until you can seamlessly go from the backbeat snare accent on the &’s to the fill pattern. Work on each pattern individually and get as comfortable as you can with that and then try playing the whole page in sequence so that you can play each fill in turn within a two or four-bar phrase.
Here’s the PDF with a selection of patterns for you to learn. I hope you enjoy working on this. Let me know how you got on.