When you say your command, you can have the MOVI write a pin to HIGH which will trigger the sound.
I did this with my Central Command Hub project but I used a Raspberry Pi instead of an MP3 Module.
If you’re interested you can refer to STEP 5 of the tutorial I made on Instructables.
You can also check out this forum where I posted my question of how to get the Movi and the Raspberry Pi to work together. It should give you a better understanding of how it works.
Hope this helps.