It isn't a parts to be replaced kind of issue, you , or someone there, set trays as dedicated.
as admin go to Machine Status >Tools > Device Settings >Paper Management > Tray Settings and set them to Adjustable
Have you replaced MD PWB ( MCB ) with the correct part no. 960K55090? I ask because there is another part for lower speed of machine (7525,7530, 7535)?
If yes, it remains to be replaced 960K54150 Tray Module PWB.