Vielleicht geht s ja so. Sofern immer nur 1 Suchergebnis pro Zeile erwartet wird.
Sub Schaltfläche1_Klicken()
Dim i As Long, raFund As Range
With Worksheets("Tabelle2")
For i = 1 To .Cells(.Rows.Count, "A").End(xlUp).Row
Set raFund = .Range(.Cells(i, "C"), .Cells(i, .Cells(i, .Columns.Count).End(xlToLeft).Column)) _
.Find(what:=.Cells(i, "A"), LookIn:=xlValues, lookat:=xlWhole)
If Not raFund Is Nothing Then
raFund.Value = .Cells(i, "B").Value
Set raFund = Nothing
End If
Next i
End With
End Sub