how can we go to repulsebay beach from yuen long, hong kong?

You can take West Rail Line at Yuen Long Station, and get off at East Tsim Sha Tsui Station, Exit J. Then take public bus no.973 at New World Centre, Salisbury Road, and get to Repulse Bay Beach, Repulse Bay Road. The whole way takes around 105 mins on the way. And the ticket fare is 33.3HKD per person.
After arriving, walk south around 275 yards and arrive at the destination.