I'm a little confused on what exactly your question is but I'll try.
Method 1 = find a RD you like, mute all but the drums, title the song, then save it. On play back you will only have the drums.
Method2 = loop within a RB - highlight the measure(s) you wanted repeated, click on the loop icon, then click on play and loop highlighted area.

I hope this covers your request and good luck.

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Life is short so make sure you spend as much time as possible on the Internet arguing with strangers.

64 bit Win 10 Pro, the latest BiaB/RB, Roland Octa-Capture audio interface, a ton of software/hardware