TapeMaster has the option of displaying the Repository window above or below the Inventory window depending on your preference.

Open the TapeMaster preferences by clicking File > Preferences.

Set the field Volume List Above Repository List to False and click OK to commit the data and close the window

A popup declaring a restart is required for the change to take effect will be displayed, click OK to close the window.

Close and restart TapeMaster to effect the changes.