Do not attempt to chip tar off wooden furniture without freezing it first as this can damage the wood. The tar must be frozen either by placing a bag of ice on the stain or simply piling ice on the area. Once the tar has become hard and brittle it can be removed quite easily with a dull knife or spatula. Use gentle movements to work the stain to avoid harming the wood underneath. Move toward the center of the stain gently from the outside and repeat until the tar stain is removed. This might take a bit of work but the tar will eventually come off the furniture. Tar generally leaves a residue once it has been removed but this can easily be fixed by applying vegetable oil to the stain with a clean cloth. Gently rub the stain until it disappears.
Petroleum jelly is an effective method for cleaning tar off leather and can be applied with a soft cloth and then wiped off. While this method is normally used on leather car seats it can be applied to leather furniture in the home as well. Cuticle oil is also considered an effective method, but it's important to keep the oil on the stain and off the leather couch to prevent further staining.
Act quickly while the stain on your upholstery is still wet for best results. If the stain has hardened the following methods are still applicable. Blot up excess liquid from soft tar with a paper towel. Scrape the tar off the upholstery with a butter knife or soft plastic spoon, taking care not to pull on the material too much. Wetting a cotton ball or paper towel with rubbing alcohol and dabbing the stain should lift the whole stain. Be sure to apply the alcohol only with a paper towel or cotton ball to avoid getting the surrounding upholstered material wet and possibly damaged. If the stain is still there after using the rubbing alcohol, try dabbing at the stain with a water-wet paper towel. Once the area is damp use another paper towel to dab at the stain with detergent. Repeat as necessary.