What is the objective of your simulation? If you’re trying to find out how heat propagates throughout the entire brake disc and its dissipation you can do that with “Heat Transfer” under “Thermostructural”. If you refer to what @vgon_alves has kindly posted, pointer 3 will allow you do so with relative ease.
However, if you want to determine how heat propagates from the brake disc to another fluid, say a brake disc submerged in water, then “Conjugate Heat Transfer” is the mode you want but I doubt that would be the objective and if so it would be rather unusual considering the practical application of brakes.
With that being said, you new geometry titled “geom” is broken as you have intersections and hence that is why you are unable to mesh. You need to clean up the geometry properly before you can mesh it. The broken areas are clearly seen in the diagram below where the blue part is intersecting with the grey part.
Do determine what your objective is and then fix your geometry accordingly before attempting to mesh again.