What model? In general, on the Marantz units I have worked on, remove knobs, remove corner screws and retaining nut to remove faceplate, Smokey dial cover and bezel come off with faceplate. Lift dial pointer off of its track (careful! The dial pointer is brittle with age and very fragile.) Remove small screws that hold plastic dial face to chassis. Gently pry dial plate off of chassis - it may have adhesive between it and chassis. The velum is on the back of the dial face and attached with adhesive. Remove velum and use isopropyl alcohol and cotton swabs to remove all old adhesive. I use a product called iCraft SuperTape or Thermoweb Supertape in 1/8” width to adhere the velum to the dial face and to adhere the dial face to the chassis. It is a strong, thin double sided tape available on Amazon.
Use 48# translucent white velum. Some people use two layers, especially if they are using LED’s. I generally don’t. Once it is taped to the dial face, place another layer of Supertape and stick dial face on chassis so that the holes for small screws line up. Replace the small screws that hold dial face to chassis. At this point, you should remove the rear covers from the meters and remove the yellowed velum from them. Use the old pieces as a pattern to cut new velum pieces for the back of the meters. I use small pieces of masking tape at the edges to secure the new velum to the meters. Replace the cans on the back of meters, replace dial pointer, replace faceplate and knobs. You should be good to go.
This is from memory, which is not always reliable. If anyone sees an error or a better way to do it, please chime in.