first you must creat a preset in preset management,name it and assig it to watever midi channel you want ie 1 in the master global mode,once done go to sample management
select the sample you want to assign and presse 6 pplace sample.presse enter 2 time chose g1 g2 g3 wherever you want to assign it (usually one octave) and select the lower key (the lowest note of your region and the highest note then press enter.
once it's done go back to the master mode and check that you assign the right preset to the right midi channel
don't you have the manual??