Code:
'search for a particular line and do something with it
'read the file into an array
'find the line you are looking for
' then read the array back into the file using Output
'so you can overwrite the original file

Option Explicit
Option Compare Text
 

Private Sub Form_Load()
    Dim myArr() As Variant, myLine As String
    Dim myComp As String
    Dim i As Integer, intNum As Integer
    
    myComp = "The line I am Looking for"
    intNum = FreeFile
'
'open file
    Open "C:\myfile.txt" For Input As intNum
    
   Do While Not EOF(intNum)
        i = i + 1
        ReDim Preserve myArr(1 To i) As Variant
        Line Input #intNum, myLine
        myArr(i) = myLine
       
        myArr(i) = Trim(myArr(i))
        If myArr(i) = myComp Then
'do whatever you want to here I change it to read "My Fixed Line"
        myArr(i) = "My Fixed Line"
        
        End If
        
    Loop
        Close #intNum

 'open file and save new contents
 
    Open "c:\myfile.txt" For Output As intNum
        For i = 1 To UBound(myArr)
            Print #intNum, myArr(i)

        Next
    Close #intNum
End Sub