Have you come across the concept of error checking? You are performing two operations in the statement that starts will my $LastCol. First you are getting a value (hash ref or undef on failure), then you are extracting data by derefing the return value. Something like this should work:

my $LastCol = $sheet->UsedRange->Find({
    What => $searchstr,
    LookAt => 2,
    LookIn => -4123,
    MatchCase => "False",
    SearchDirection => $searchdir,
    SearchOrder => xlByColumns
});
return $LastCol ? $LastCol->{Column} : undef;
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You also have a typo in the post as it should be ->{Column}. And -4123 looks like a constant to me so you should not be hard coding it. Same for the LookAt => 2 probably.

use Win32::OLE::Const 'Microsoft Excel';
my $x = Win32::OLE::Const->Load("Microsoft Excel 9\\.0 Object Library"
+);
for my $key ( sort { $x->{$a} <=> $x->{$b} } keys %$x) {
    printf "$key = %s\n", $x->{$key};
}
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