I've never done it for chowder but I do make stew. I use flour or cornstarch as a thickening agent for things. Heat up the chowder on the stove. Put a few tablespoons of flour or cornstarch in a bowl and mix in just enough water that you can make it smooth and are able to pour it into what you have on the stove then slowly add it to the soup/chowder. Stir it regularly while whats in the pot thickens. If after a few minutes its still runny, repeat the steps until you get it where you want it.
Be careful though because too much of either thing may change the flavor. Taste it as you go. (=
at 7:44 PM on Dec. 31, 2009