If you sort your data where the non blank value of Column A is always first, and then select all Column A rows
You can right click on the value for row 1 for Column A and select

Here is a alternative JSL solution

Names Default To Here( 1 );
// Create the sample data table
dt = New Table( "Example",
Add Rows( 5 ),
New Column( "Column A",
Character,
"Nominal",
Set Values( {"A", "", "B", "", "C"} )
),
New Column( "Column B",
Character,
"Nominal",
Set Values( {"Apple", "Apple", "Banana", "Mango", "Mango"} )
)
);
// Sort the table to allow non black Column A rows to be first
dt << Data Table( "Example" ) << Sort(
By( :Column B, :Column A ),
Order( Ascending, Descending ),
Replace Table( 1 )
);
// Modify the Column A
Hold = "";
For Each Row(
If( :Column A != "",
Hold = :Column A,
Show( Lag( :column b ), :column b );
If( Lag( :Column B ) == :Column B,
:Column A = Hold
);
)
);
Jim