First I would recommend updating to the latest 3.5.x patch version by downloading it here, unzipping it directly into your MusicBee directory and letting it overwrite existing files:
https://getmusicbee.com/patches/MusicBee35_Patched.zipTo access the pitch control, go to Preferences/Player and hit the Equaliser & DSP button in the lower right corner. Then, in the DSP Plugins list, select the "Tempo Control" choice; this will bring up a window allowing you to change either the "play speed" (Tempo), pitch, or sample rate.
For the 432 Hz effect, select pitch, type -0.32 into the semitones box, and hit OK.