Question about Wahoo Kickr Core

As @richiamman said, simply turn until it fits. Then tighten with the appropriate tool, without which it is unfortunately not possible.

If the cassette has play: According to "Drivetrain Compatibility [CORE]" (https://support.wahoofitness.com/hc...), the 1.8mm spacer ring must be fitted behind the cassette for cassettes with more than 34 teeth.

Should of course be "with more than 32 teeth"...

I also have a 105 cassette on it 34-11. works tiptop.
make sure you turn the sprockets until they fit. it has a groove so that the sprocket only fits in one position (rotating around its own axis).
GCN has a video on this