how do I open the unlocked driver's side door?

Hello, I’m Pete from the Car Genius team at RepairPal. I’m sorry you’re dealing with this concern on your Buick Park Avenue. Since the driver side door is unlocked but will not open and if it will not open from either the inside or the outside door handle this can indicate a fault with the door latch itself failing to where it may need to be replaced. When a door is stuck closed like this with no way to open it using either handle this usually involves a lock smith coming out and using their tools to open it or to have the interior door paneling removed with the door closed (which can lead to a damaged interior door panel assembly) to try and then manipulate the door latch itself to open it. Unfortunately, there is no easy way to open it when it is stuck like this. I wish I had some better news to give you. You can also have a local reputable shop look into this concern as in many cases they can usually open it using their tools as well. If you’d like to find a trusted, certified repair shop in your area, you can check here: https://repairpal.com/certified. If you need more advice, or have any further questions about your vehicle, we’re here to help. Just give us a call at 877-913-1554 where we will be happy to assist!