You can use iCal, a third-party application to do Yahoo calendar sync for Android.
Sign in Yahoo calendar website. Additionally, choose "manage calendars" from the drop-down menu. Next to the "calendars" is a gear. Additionally, tap "Share" from the drop-down menu. In the "to-do" or "calendar" tab, choose your schedule. Continue by using the spacebar. You must select the URL under "share with iCal address." By hitting the "CTRL + C" key, copy the iCal address of the Yahoo calendar to the clipboard. Choose a copy of your calendar by clicking on the link. Moreover, to apply your changes, press "Save". The box should be shut. https://www.yahoosupport.co/blog/yahoo-calendar-sync-for-android/