Reversible reactions proceed in both directions.
For eg X + Y <==> Z
At any one point in time, there would be X, Y and Z in the reaction mixture. When the proportion of X, Y and Z in the reaction mixture becomes constant, a state of equilibrium is achieved. Enzymes do not cause a greater amount of Z to be formed, they only cause the equilibrium state to be achieved faster.
An example of enzyme catalysing reversible reactions is carbonic anhydrase which would be covered in greater detail in the topic 'Transport in Humans'.
carbonic anhydrase
carbon dioxide + water <==> carbonic acid