Go to Setup->Load... and load a setup in the Level (Noise) section as shown below.
How to use WinMLS as a level meter for measuring SPL values in octave, 1/3 octave, dBA?
How to find the level of a measured impulse response (for example in dBA)?
How to display the level in octave bands?
How to display the level in dBA?
How to display several measurements (e.g., for comparison and for saving the data)?