Immersion after Rosh Hashana

If a woman needs to immerse in a mikve in the evening after Rosh Hashana, which laws apply to her, and when should she do all the preparations? Thank you very much

A woman who needs to immerse in a mikve after Rosh Hashana can eat meat on Rosh Hashana like she normally does. (On regular days a woman should avoid eating meat on the eve of the immersion.) But on Rosh Hashana, when it’s a commandment to enjoy a meat meal, she’s allowed to eat meat. She’s also allowed to put on makeup before the holiday, since that makes her holiday more joyous. After Rosh Hashana is over, she should check her teeth thoroughly and wash off all the makeup.

As far as the preparations for immersion are concerned, the “Shulchan Oruch” rules that they should mainly be done before Rosh Hashana. On the night of the immersion, she should once again take a worm bath and check her whole body for things that might prevent contact with water.

Shulchan Oruch, section Yore Dea, ch. 199, §6