[HELP!!!] Creating Transaction History Spreadsheet

Hye everyone. I'm trying to develop a spreadsheet to keep track my bank transaction activities.
Right now I'm having a little bit problem and I really need your help to figure out on how to do it.

So here's what I'm planning.
Untitled.png

in the column 'bank', we can select the type of bank that we are interested in, and then when we click the bank from the drop down list, the column 'balance in bank' , the value in that cell will appear from the reference table that (green table).

program excel.JPG

as you can see, CIMB will calls value 250 from green table, BIMB calls value 300 from the green table.

however, when calculations been made, there will be new balance in the bank accounts. this the part that I do not know on how to program it. any ideas on how can I update the reference table everytime 'NEW BALANCE' is calculated for certain bank ?