effects

This is a mode thing more than an Effect thing.

If you press the Gobo encoder down you'll get to the "modes" for the Gobo wheel.  There should be at least one that says rotate.

Then another wheel should control the spin speed.

I find the ML control display easier for many beginners. All the options, buttons and settings are in one place. It's slower and you need to see screen and stage at the same time, but easier to understand.

Select one or more fixtures then Displays> soft-key "ML Controls"

As Patric said it's not an effect. Gobo rotation is a function of the light so it has it's own control in the channel. You might use an effect to have the fixture change the gobo every so often, or speed up/down the rotation in a pattern.

Not at the desk so this is from memory

On the MAC's, assuming a basic profile in the Ion patch, it's in the Image section, the 2nd encoder wheel selects the image, you can press down on the encoder and hit Next/Last to select the gobo's that can rotate.

Once you've selected a rotational gobo, the 1st encoder wheel should say "Gobo Ind/Spd'.  You can spin the encoder wheel to get movement, I think -100 to 100 is one direction, 0 to 100 the other, or something like that. If you don't see "Gobo Ind/Spd" on encoder 1, press down on the 2nd encoder and then press the Mode softkey to get the 1st encoder into the correct selection.