PREVIEW - Assign profile

[bigscreen]

I run MAC OS 10.14.6.
I have scanned some black and white photographic negatives which are produced in Grayscale.
I need to submit the images to photographic software which requires that the images be in an RGB profile.
I go to Preview and select "Assign Profile " and expect the options to include "Colour Sync Profile" but I am offered only other Grayscale options.
Does anyone know where I can convert JPEG black/white grayscale images to a colour sync?

 

[ferrarr]

You may have to open the files in an image editing app like Photoshop (Adobe), Photo (Affnity) or even Gimp (FOSS). convert it in the app and save as different file type (TIFF, PDF, etc.). Then "save as" JPEG if you need the file to be a JPEG.