how can we go from thim sui mtr to repulse bay beach by metro train in Hong Kong?

MTR cannot take you to travel between directly and transfer is needed, so bus shall be a better way. Walk from Tsim Sha Tsui (I presume this is your starting site) to Silvercord, Canton Road to take bus no. 973 and get off at 127 R B Road. After getting off, you would be at the bay.