How to Opt into Google Play Store Signing for aab file

Hello, it has been a long time i updated my app and now that i am trying to do so, playstore is asking me to opt into their signing process. i need help, a comprehensive process on how to do this. is there any tool that coverts my android.keystore to what playstore requires or how do i go about this. anyone who has already done this should please help me.
i have searched the forum but i still did not get anything comprehensive.

please I need a response to this someone should please help.