Same idea for multiplication: (a × b) mod m = ((a mod m) × (b mod m)) mod m.
Example: (23 × 19) mod 5. Direct: 437 mod 5 = 2. Modular: (23 mod 5) × (19 mod 5) = 3 × 4 = 12, then 12 mod 5 = 2.
This prevents overflow in products. Take mod after each multiplication to keep numbers small.