Transferring Apex Legends Account on Steam

Heya,

Steam accounts can only be linked to one EA Account in their lifetime.

You can only link one Steam account to an EA Account, so make sure you choose the right EA Account to link to.

From: https://help.ea.com/en/help/pc/link-ea-and-steam/ 

This means that a new Steam account can be linked to an EA Account, but if that Steam account has already been linked to another EA Account, then you cannot link it to another EA Account.

So in your case, it would sadly enough not be possible, considering both Steam accounts have already been linked to an EA Account.