Wahoo Kickr with a 10 speed cassette but my bike is running Shimano 11 speed, just fit an 11 speed cassette?
Presumably the Kickr has a '10 speed' 34.95mm freehub body rather than a '11 speed' 36.75mm one.

Some wider-range 11 speed cassettes come with a 1.8mm spacer and will in fact fit on a 10 speed freehub body. The larger sprockets allows the spider to overhang the inboard end of the freehub body without the sprockets interfering with the spokes (which you of course don't have on the trainer).