Not the 220 volts, that's fine
Be careful here. Your hot tub probably has a 240-volt supply for the heating elements, but the pump motor may still be 120 volts. It's the same with U.S. ranges and dryers -- They use the full 240V for heating but have 120V for the timers, motors, etc. Does the tub connect to the supply via a 3-wire or a 4-wire cord and plug?
but I think it's the hertz frequency that can't be changed?? This effects US appliances that have rotating parts - they break down sooner.
Transformers change voltage, but can't change frequency. Some types of motor are sensitive to the frequency, with others it will make little difference. The tub motor is most likely an induction type which
will be affected, but it's quite possibly borderline. Running on the lower frequency (50Hz U.K. vs. 60Hz U.S.) will result in lower efficiency and possibly a little extra heating in the motor. For smaller motors in appliances which are run for short periods this is of little consequence, but it becomes much more significant with larger motors, particularly those which will run for longer as in this application.