Update your post to include full system hardware specs and full OS information.
Make and model monitor? How is the monitor connected to the computer?
Right click the small speaker icon usually located in the lower right screen corner.
A menu should open with multiple sound/audio choices that in turn lead to quite a number of Windows, tabs, and properties.
Most likely you simply need to make the necessary audio configuration changes.
But do double check all of physical audio connections as well. Ensure that the monitor's speakers are enabled via the monitor's configuration menus.