Its labor intensive and there is a learning curve

If the stucco has been painted, clean the surface to be repaired, chip off any irregularities.
Purchase some stucco color coat product and a sponge applicator, mix to a medium thick consistency and apply.
When dry,paint to match.

If the area has not been painted, the process is the same.

Except that, you purchase "add-mix" color that is available.

There are also vendors, other than the big boxes, whom, if you bring a sample, will blend for you.