With VoiceOver running, turn on in Settings, Accessibility, VoiceOver, Hand Gestures.

Once turned on, activate when watch is waken with a double clench of your fist (need to do this every time watch is woken up).

When on:

double pinch (thumb and index finger twice) move previous item,

Single pinch (thumb and index finger once) next item,

clench (fist once) activate item, and

double clench (make fist twice) Digital Crown function.

Handy for the workout app.