After August 5, users won't be able to access the old Yahoo Messenger, and it is recommended to transition to the new Messenger apps on web and mobile.
Here's a link explaining how the new Yahoo will work.. and to install it:
On mobile - https://mobile.yahoo.com/messenger
On your computer - Go to messenger.yahoo.com in your browser, or chat right from Yahoo Mail.
To add me to Yahoo my ID is BellaDaisy22xo