Kindly refer to the following links:

https://www.assimalhakeem.net/when-someone-says-jazakallah-khayr-is-it-sunnah-to-reply-baarak-allaah-feek-for-male-and-baarakallaah-feeki-for-female-or-is-it-sunnah-to-reply-wa-iyaak-for-male-and-wa-iyaaki-for-female-or-sunnah-i/

How to thank people


Should we say Jazak Allah or Jazak Allah Khair? | Sheikh Assim Al Hakeem



If someone says Jazakum Allahu khairan to you:
You can reply: Wa antum fa jazakum Allahu khairan

Or: wa yaakum


fem: Jazaki Allahu khairan -wa yaaky
masc: Jazak Allahu khairan -wa yaak