Convert some images to grayscale, but leave others color?

I have a multi-page pdf. Each page has 36 products, with a picture and a barcode (see below).

The printer needs us to convert the barcode to grayscale. It is currently RGB. The barcode won't scan unless it's in grayscale.

The only way I've figured out to do this is to go to "Edit PDF," click on the barcode, select "Edit Using" and open in Photoshop and convert it there.

Doing it this way I'm only able to convert one barcode at a time. With 36 barcodes per page, and a document that is about 50 pages, this seems very daunting.

Does anyone know of a different way to do this?

Thank you!