When do I go to the mikvah if I’m supposed to go Tuesday night
We do not go to the mikvah on Yom Kippur eve, since we do not wah ourselves on Yom KIppur, therefore you will go on Motzei Yom Kippur. The preperations should be done similar to when you go to the mikvah on motzei shabbos.
Have a gmar chasima tova
Shulchan Aruch O:CH 613-12,