Scrape excess food off the chair with a butter knife or your hand immediately. Blot excess liquid with a paper towel or a clean rag.
Test an unseen area of the upholstery by dabbing on a little cleaning solution with a rag or paper towel. Dry cleaning solvent is generally safe for cleaning upholstery and works well against fat-based stains such as oil or butter. A mixture of 1 teaspoon of mild detergent to 1 cup of water works on many stains as well as isopropyl alcohol and a 1-to-1 solution of vinegar and water.
Dab on cleaning solution with a rag or paper towel, working from the outside of the stain inward. Dab and blot the stain carefully. Do not rub.
Dab the cleaned area with water using a clean damp rag to remove the cleaning solution. Work from the outside the stain inward, dabbing on water and blotting up the water and solution.
Use a handheld upholstery cleaning machine for large stains and regular maintenance.