Mix a cleaning solution of 1 quart lukewarm water, 1/2 teaspoon heavy-duty detergent and 1 tablespoon white vinegar. Pour the cleaning solution into a spray bottle.
Place an absorbent towel around the stained area on the upholstery to avoid further staining by containing the stain during the cleaning process.
Spray the blackberry juice stain on the upholstery liberally with the cleaning solution.
Rinse the blackberry stain by applying a towel soaked with clean lukewarm water to the stained area to thoroughly wet it.
Dab at the stain lightly with a clean portion of the wet towel.
Scrub the rinsed area by sponging it lightly from the center of the stain to the edge with rubbing alcohol.
Rinse with a towel soaked in clean warm water placed onto the stained area and allow it to set for 30 minutes, occasionally changing it to a clean position.
Direct a fan onto the rinsed area and dry it thoroughly before using it.