A brief blurb on the official APB forums outlines all the details. Players will need to have an open character slot on their G1 accounts as well as their old RTW login credentials (the process involves logging into the RTW account to initiate the transfer).
GamersFirst notes that this is not a comprehensive restoration. "The main items being restored are clothing and symbols. Please understand that no progression, APB cash, RTW Points, Action Time, weapons, or vehicles will be restored," says the post. Also, only two outfits are being restored due to technical issues (though any symbols and clothing items used in other outfits will still exist on your character). Check out the APB forums for more.