Hi I have a following problem

Let us assume what i have Excel sheet with two columns A and B

Current situation Wanted result
A B A B
Hs Hs Hs Hs
Kht Undef Kht Kht
HsMr Hs HsMr HsMr

I want to make a macro which copy/paste or replaces values in column B
based on cell location in column A, So if the cell value in column B
is Undef the value Undef in column B should be always replaced by
value of cell beside from column A. E.g If macro founds the value
"undef" or Value "*Mr" in column B it replaces these values in column
B on basis of values found in column A beside that particular cell.

Any ideas or related code to solve the problem?