Put on middle ring.
Screw adjuster all the way in then back out 1/2 turn.
Screw in L screw far enough so that the the DER won't shift to the smallest ring. (rear on smallest cog)
Shift SHIFTER to lowest gear

With bike on stand or someone holding the rear, slowly pedal.
Back off the L screw 1/4T at a time until chain drops to smallest ring. Turn another 1/4-3/8T.
Loosen cable clamp & pull the slack out of the cable semi-firmly and reclamp.