This is Remix Deck C Sequencer mapping for the Midifighter Spectra. 

If you have Midifighter 3D than see this mapping: https://maps.djtechtools.com/mappings/6408

Please check the visual layout below to to see how your side buttons are mapped. All 4 Sample Slots of Remix Deck C are built in to the mapping - to select one of 4 Slots hold down your left or right-handed center side button and press one of 4 buttons on the top row. 

Complete controller diagram is here: https://imgur.com/YzY7q47