There are some unused declared variables and some undeclared used variables. I think if you want to declare variables, you should set the option explicit at top of your script.
What about:
;Script Options
If Not @LOGONMODE
    Break On
Else
    Break Off
EndIf
Dim $RC
$RC = SetOption("Explicit", "On")
$RC = SetOption("NoMacrosInStrings", "On")
$RC = SetOption("NoVarsInStrings", "On")
If @SCRIPTEXE = "KIX32.EXE"
    $RC = SetOption("WrapAtEOL", "On")
EndIf

;Declare variables
DIM $csv,$csv_array,$read,$cintndc,$balsndc,$cintproc,$balsproc,$Total
DIM $Handle1,$ColumnAccount,$ColumnBalance1,$ColumnBalance2

;Initialize variables
$csv="C:\temp\test.csv"
$ColumnAccount=5
$ColumnBalance1=71
$ColumnBalance2=66

;Code
RedirectOutput("C:\temp\output.txt",1)

$Handle1 = FreeFileHandle()
If Open($Handle1,$csv) = 0
    $read=ReadLine($Handle1)
    While @ERROR = 0
       
        $csv_array=Split($read,"|")
        If UBound($csv_array)

            ;Add together first balances
            ? "Account:  " + ($csv_array[$ColumnAccount]) + "   Balance:   " + ($csv_array[$ColumnBalance1])
            $cintndc = Round($csv_array[$ColumnBalance2],2)
            $balsndc = $balsndc + $cintndc
            ;$balsndc ?

            ;add together second balances
            $cintproc = Round($csv_array[$ColumnBalance1],2)
            $balsproc = $balsproc + $cintproc
            $balsproc ?

        EndIf
        $read=ReadLine($Handle1)
    Loop
    $RC = Close($Handle1)
   
    @CRLF
   
    ;add together first and second balances
    $total = $balsndc + $balsproc
    "Total balance is: " + $total?
EndIf

RedirectOutput("")

;Personal UDF Section

;UDF Section