If you want to decrease the amount of C6 H12 O6 in your diet, what food should you decrease?

All foods especially carbohydrates which are converted to glucose in the body for energy. They are:
complex carbohydrates (fruits, vegetables, starch and bread products)
simple carbohydrates (table sugar, honey, candy, syrup)

Protein is also converted to glucose when needed.
Fat is a poor source of glucose.

https://www.ghc.org/healthAndWellness/?item=/common/healthAndWellness/conditions/diabetes/foodProcess.html

Glucose is a six-carbon sugar represented by the formula C6H12O6. ...
https://www.saylor.org/site/wp-content/uploads/2010/11/BIO101-Carbohydrates.pdf