Forms :: DLookup - Changing Value In A Form

I'm making a form for colleagues to use which will eventually populate a table. I'm using DLookup to populate some of the fields in the form from another table. The problem is that for a few of the fields in that other table, the values are incorrect.

(Obviously the most sensible thing to do would be to amend the source data but for various reasons I cannot do that.)

For example, "date built" in the original table might be "f" but that needs to be changed to "h", so I tried the following but it doesn't work:
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If DLookup("date_built", "dbo_meas_questionnaire", "[meas_id] = Forms!FrmRetestSearch.numOrigId") = "f" Then
Me.TxtDateBuilt = "h"
Else
Me.TxtDateBuilt = DLookup("date_built", "dbo_meas_questionnaire", "[meas_id] = Forms!FrmRetestSearch.numOrigId")
End If
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