I don't have a kickr but does this help?

https://www.trainerroad.com/...ed-confirmation/6102

or this:

https://support.wahoofitness.com/...reehub-Installation-

or this:

https://forum.slowtwitch.com/...RAM_AXS%3F_P7167361/

I have 2017 Kickr. Those only work with 2018.

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The curious task of economics is to demonstrate to men how little they really know about what they imagine they can design.

https://rotorbike.com/...-speed-cassette.html

http://www.sunrace.com/en/products/mz-12-speed

12s cassettes that fit on HG freehubs. Not cheap options (particularly Rotor).

Rotor is good option but when I looked into it, the 11-36 (smallest option) will cause me to exceed the FORCE AXS RDR teeth capacity.

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The curious task of economics is to demonstrate to men how little they really know about what they imagine they can design.

Hey,

I can't tell you how to install a 12sp AXS cassette on a Kickr but what I can tell you is that the AXS works on a 11sp cassette with no issues in ERG mode. I have a Tacx Neo with a 11-24 11sp cassette that I use for my Tri bike which is Shimano 11sp and my new road bike which is SRAM AXS....If I really want to use resistance mode I can still do that by avoiding the two outside cogs on both ends.

It is certainly not ideal but works more than good enough for me that I don't bother to change cassettes at all.

Good luck and happy riding. By the way I really like the AXS Force on my road bike....no regrets going 12sp at all (at least for me).
Uli