Use a regEx:

my $str = '12-12 WANG 28 Jul H PRG SPEC 1320m Bk past midfield wide,bt
+n car top T J Bau 57 (12) 7/7 Wnr: VENUS SERENA 1:26.82 13.5L';
my ($str1, $str2) = $str =~ /^(.*?)(Wnr:.*)/;
print "$str1\n$str2\n";
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