Hatsune Miku: Project DIVA Mega Mix Screenshots on Nintendo Switch

so  you're  probably  equipping  a  "module"  to  "shared  set",  press  down  on  the  right  joystick  until  it  reads  "song  specific"  in  the  lower  right-hand  corner,  then  hit  x  to  customize  and  then  change  the  outfit  for  the  "song  specific  set"  rather  than  the  "shared  set  A/B/C"  
hope  this  helps!  (also  if  you  are  in  the  module  screen  if  you  press  ZR  and  ZL  together  itll  take  you  right  to  the  recommended  module  for  that  song!  )