I heard that there is one train from Hanoi to Nanning every other day. But i can not find the information. Maybe you can contact a travel agency in Hanoi and they must know it.

I think there is train from Hanoi to Nanning. It will be helpful if you ask the Vietnam side.

Ms. Sharon, please refer to the following information.

Chinese train between Hanoi and Nanning:
T871 departs at 18:15 in Nanning and arrives at Hanoi at 07:00 the next day;
T872 depats at 20:25 in Hanoi and arrives in Nanning at 10:05 the next day.

Vietnam train between Hanoi and Nanning:
MR1 Hanoi/Nanning 20:25/10:05 the next day
MR2 Nanning/Hanoi 18:15/07:00 the next day