I understand what you want to do is
If the part number in column A is included in the Description in Column B in the same row then
Replace that part number in Column B with an asterisk "*"
Otherwise leave the description alone.
You can do this with a worksheet formula, if you can accept not changing the information in col B also. For example, with your data in columns A & B
and fill down as far as required.
If you really want to change the information in Col B, you could either copy the results in Col c, the Paste Special Values over Col B; or you could use a macro:
To enter this Macro (Sub), <alt-F11> opens the Visual Basic Editor.
Ensure your project is highlighted in the Project Explorer window.
Then, from the top menu, select Insert/Module and
paste the code below into the window that opens.
To use this Macro (Sub), <alt-F8> opens the macro dialog box. Select the macro by name, and <RUN>.
Dim rSrc As Range, c As Range
Dim rw As Range
Set rSrc = Range("A2", Cells(Rows.Count, "A").End(xlUp)).Resize(columnsize:=2)
Application.ScreenUpdating = False
For Each rw In rSrc.Rows
rw.Cells(2) = Replace(rw.Cells(2), rw.Cells(1), "*")
Application.ScreenUpdating = True