You may not have much success with this. The products that Carpet Cleaners use are very high in acid and 50% of the time they don’t even work.
However, I have seen this work on occasion and it’s worth a try.
Step #1: Saturate the spot with Lemon juice and allow it to dwell for 5 minutes.
Step #2: Blot up the area with a paper towel.
Step #3: Apply a small quantity of cleaner to the stain. (To make the cleaner solution – mix 1/4 teaspoon of a hand dish washing detergent such as Dawn® or Joy® with a large cup of water) Use a blotting motion to work the cleaner into the affected area. If the stain is being removed continue applying detergent and blotting with a white paper towel until the stain is gone.
Step #4: If the stain is still there, flush with water to remove the cleaner, blot with paper towels and then let this stain rest until the next day. At this point the carpet fiber needs to rest and dry. You have done a great job in preparing for step #5 the next day.
Step #5: The next day, if the stain is still there: You are going to use a very common household product of 3% Hydrogen Peroxide. Moisten the stained area with the Hydrogen Peroxide (using a spray bottle) and let it stand for one hour. Repeat this one hour later if necessary. If any staining remains – Agitate, rough up the area with a paper towel, spray once again and then put a folded paper towel on the stain and a weight like a brick on top of the paper towel and let stand until the next day.
NOTE: Light will cause peroxide to change back to water so no rinsing is necessary.