Go to Library > Expression Maps…, and on the top of the window that opens, press Expression Map Data. Set Microtonality Playback to Pitch bend. Make sure that the Pitch bend range is the same in Dorico as in your synth. Alas, Dorico doesn’t support MPE. This is monophonic pitch bend so you can’t have chords (where the notes have different microtonal inflections) on a single track. Each voice has to be on its own MIDI channel.