What should I do if Antifreeze got into the transmission?

Under such conditions, you have no coice but to flush the system.

Leakages is most probably from the cooler/heater core inside radiator. You would have to get it replaced first.

The anti freeze leaked in by mistake speed sensor o ring was not seated all the way when doing thermostat coolant system maitenance. Next day there was a bad engine shutter while driving. Could the coolant affect the gear box that quickly? Is there any way to do a flush at my home? If so what do I need?

Under this situation, there should not be much antifreee in transmission fluid and if the the fluids are not pink colored, you need not flush it. Replacing the fluids would be sufficient and the little antifreeze would soon evaporate.

Run the engine to warm up the transmission fluid and drain it.
Replenish the fluids and repeat until the fuids are bright red and you should be good to go.

As to the stutter, it could be someting else that is related to the engine. Check the distributor cap for presence of condensation. Check the spark plugs and wires.

I don't use transmission fluid in my transmission I put in 10/30W.

You mean it is a manual transmission? In thst case there is nothing to worry about. The antifreeze is not going to affect anything.

Phew!! that was a relief!! Thank you so much!!

You're welcome.

Have a nice day.