Actually, if it's a 121 SD, the story is a bit different.
ANYWAY - always align a SD by bypassing the switch and directly connecting the outboard (stand-alone) LNBF. For a 105 SD that's the 119, and for the 121, it's 110.
If all you have is a dual-tuner receiver, then connect that LNB to port
1 of the DP34 so you can feed both tuners.
Next, go for the FSS (105 or 121) LNBF - going through port 1 of the DP34 if you have to.
The final DP34 config should be 119=1, 110=2, and FSS=3.