How do enzymes lower activation energy?
Weakening of bonds in the reacting molecules is the main reason. See the explanation...
If you think in terms the "lock and key" model of enzyme action, when the reacting molecule(s) fit into the active centres of the enzyme, the bonding with the enzyme structure weakens bonds within the reacting molecules. This lowers the energy needed to break the existing bonds, and lowers the activation energy as a result.