How to fill in empty cell from another data set

[CHYT]

I have one set of data which some some missing account name in which another data set can provide the information. 

May I know how I can fill in the data while keeping the last two column in Data set 1? Thanks.

Data set 1: 

Data set 2: 

[Qiu]

@CHYT 
We can think more if we have more sample data.

For your current particular case, we could use a Join tool to do it.