For "small" document the following might work (replace new_amount with actual value provided as a parameter or something like that)
'#
'# declare
'#
Dim lngFound As Long
Dim lngStart As Long
Dim lngAmountStart As Long
Dim lngAmountEnd As Long
Dim rngContent As Range
'#
'# initialise
'#
lngStart = 1
Set rngContent = objWord.ActiveDocument.Content
'#
'# loop though the contents
'#
lngFound = InStr(lngStart, rngContent.Text, "Amount")
While lngFound > 0
'#
'# find the currency symbol
'#
lngStart = lngFound + 6
lngFound = InStr(lngStart, rngContent.Text, "$")
'#
'# determine the starting position of the amount taking into consideration
'# that the currency symbol may be followed by a space
'#
If Mid$(rngContent.Text, lngFound + 1, 1) = " " Then
lngAmountStart = lngFound + 2
Else
lngAmountStart = lngFound + 1
End If
'#
'# determine the ending position for the amount identified by a space
'#
lngAmountEnd = InStr(lngAmountStart, rngContent.Text, " ")
'#
'# replace the existing amount value with the desired replacement
'#
ActiveDocument.Content = Left$(rngContent.Text, lngAmountStart - 1) & "new_amount" & Mid$(rngContent.Text, lngAmountEnd)
'#
'# find the next occurrence of the text Amount
'#
lngStart = lngAmountEnd
lngFound = InStr(lngStart, rngContent.Text, "Amount")
Wend
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