David,

There is no "above" in a table. There is no guarantee that the order will
remain the same.

This is how I would do it.

Make a copy of the table and name it "tblTemp".
Add a new field named "lngOrder" (type number - long)

Now you have a table (tblTemp) with three fields - Field_A, Field_B and lngOrder.

In a Sub, create varA string, varB string, Kount as integer.
(Note: change varA & varB to the proper type.)

Create a recordset, based on tblTemp.

Open the text file and read the first line.
Parse the line (to varA & varB), add a new record, use 1 for the lngOrder field.

Save the value (Field_B?) to a variable - varNewValue.
Kount = 2

Loop thru the text file,
   read line from text file
   parse line
   check if isnull(varA) then use varNewValue
   add new record
   if isnull(varA) then varNewValue= varB
   'Increment counter
   Kount = kount+1
Until text file EOF

do cleanup

Then run an Append query to append Field_A and Field_B to the Main table.

It would be easier to answer knowing the field names and having an example of
the data, but this should get you moving in the right direction.

HTH