Capturing nvidia shield gameplay in a rotating 20 minute buffer.

I have an nvidia shield k1 tablet, rooted, running Nougat with the latest OS release.
NVIDIA Shield Tablet K1 Android Version 7.0 (Nougat) Kernel Version 3.10.96+ buildbrain@mobile-u64-831 #1 Sat May 20 07:26:59 PDT 2017 NRD90M.1928188_904.2811 Shield Version 5.2 (24.29.404.153)

I am alpha testing an android game, and have a graphics bug, which the developers, who do not have a K1 have never seen. I want to record my gameplay and send the bug to them. I cannot find the instructions for how to do this – and it seems a particularly hard thing to google search for, as you end up with all the hits for people wanting to stream other games or movies on their tablet, and not people who want to stream themselves playing an android game.

Can somebody please point me at the instructions for how to do this?

If it is a 4GL bug, is this the place to report such things?

Thank you

Just in case somebody else goes here looking to find this out, I finally found the instructions here: