Attempt to log into your Yahoo Messenger using the username and password that you associate with the old contact list you are trying to find. If you can log in, you will be able to see the list. If you cannot log in, you will need to contact Yahoo customer service to find the old list.
Why was Yahoo Messenger discontinued?
According to Yahoo!, they ended Yahoo Messenger to divert time and resources to other communication tools: As the communications landscape continues to change, we're focused on building and introducing new, exciting communications tools that better fit consumer needs.2020-05-31
How can I access my old Yahoo Messenger?
You can also view your Messenger conversation history in Yahoo Mail by clicking the "Messenger" icon to open a pop-up window. From the "Status" menu, select "Conversation History" to access your chat logs.