To stop Yahoo from grouping messages by date, follow these steps:
Log into your Yahoo Mail account. On the top-right corner, click on "Settings," followed by "More Settings," from the drop-down menu, before finally selecting "Viewing emails."
Within Yahoo Mail's "Conversationss" section, simply switch off "Enable conversations." Once done, scroll down and click on "Save." By disabling conversation view in Yahoo Mail, your messages won't be organized chronologically; they will instead appear individually within your inbox.