@ZameldaYou will get the prompt to merge your accounts on the main menu before logging in to the lobby on Apex Legends. If you didn't receive the notification for cross progression, have no worries.
I myself am still waiting for the prompt to show up since the beginning of the new season. We don't have an exact time lapse as to when you'll get the notification to merge your accounts.
But eventually, you will receive the eligibility to combine your accounts. Just make sure that all the platform accounts you want merged is under the same EA Account.
If you'd like more information on cross progression, you can check this guide:
https://answers.ea.com/t5/Cross-Progression/A-Quick-Guide-to-Apex-Legends-Cross-Progression/m-p/13148659#M850 
