The 3D channel model can be simulated by using the specific config file +simulation_config/tri_sector_3D.m for the 3D channel model. If you want to use another channel model then you can use other config files depending on the geometry of the netwrok, i.e. TU channel is possible to use with all other config files exept the tri_sector_3D.m.
Regarding second question, I can’t see any attached file. UEs are dropped within the cell range, if you want any specific UE distribution you can add or modify the UE distribution in +spatial_distibutions.