Except you're making much smaller dots and you only have one color to work with.
Basically, you're trying to mimic the random pattern of the film grains that make up the image.
Put a drop of spotting dye in the middle of a white saucer then put the rest of the bottle away. Dip the brush in clear water and make a small puddle of water mixed with dye part way out to the rim. Make another puddle of water and dye using the mixture from the previous puddle. Successive dilution...get it?
Blot the brush dry on a piece of paper towel then dip just the tip of the brush in the (successively diluted) puddle of dye that most closely matches the area that you want to spot over. Make some test dots on a scrap piece of photographic paper that is the same as the kind as your print is made on. This is a good thing to use some of your test strips for. Continue to make diluted or concentrated mixtures of dye/water, testing them on your scrap paper until you are satisfied with your color match.
The ability to dilute your dye to get an exact match is where liquid dye and brush win out over spotting pens. You can also choose your brush so you can make the exact size of dots you want.
When you've diluted your dye to match your print and have had a practice session, it's time to channel Georges Seurat and have at your print.
Strangely, it's not as hard as it sounds but it takes time to get the hang of it.
Make a couple of duplicate prints in case you aren't satisfied with the result of the first. I suppose you could wash the dye out, dry the print again and start over but what the hell... You should make yourself a reference print anyway. Right?