Rosh Hashanah, the Jewish New Year, began on the evening of Sept. 6 and goes until the evening of Sept. 8 this year. It is the first of the Jewish High Holy Days that will continue throughout the month.
Gentiles are not commanded to observe Rosh Hashanah. However, since it is traditionally the day on which God judges all humanity, Gentiles may participate by reading Psalms, saying special prayers and repenting for past misdeeds.
A list of Psalms to recite between now and the end of the month can be found here: https://asknoah.org/wp-content/uploads/noahide-schedule-psalms-elul-tishrei.pdf?fbclid=IwAR2DFVZuhVuLvY4xJSYBN8tI7PKrO1iA-Su0XsrjzUt-7YudLoRGM50DXQI
Suggested prayers for Noahides for Rosh Hashanah can be found here: https://asknoah.org/essay/suggested-prayers-for-noahides-on-rosh-hashanah
Have a happy and sweet new year!