The overall consensus is to not top autoflowers. High stress training is not reccomended due to the very short window of vegetative stage. You want to push as much growth as you can. Topping is a way to limit growth and direct energy to lower branches which is not needed for autoflowers.
Your best bet is to start LST (Low Stress Training) your plant. Do this by pulling down the top of the plant enough to even put the canopy. This will allow the lower branches more light and you will have many main colas growing. It’s a very good way to increase your yield. During week 3-4 on my autos, I’m constantly pulling down my plant and branches to keep an even canopy and it looks like I’ll have about a dozen main branches on each autoflower.
I hope this helps.