while or for loop will work fine but u need to use substitute command for substituting the pattern.

my $length = scalar @arr;
for (my $i =0; $i <= $length; $i++){
    $arr[$i] =~ s/<pattern>/<pattern to be changed to>/g;
}
 print "@arr";
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Or better (and more idiomatically) yet:
    s{MATCH}{REPLACEMENT}xmsg for @array;


(Note that the //g regex modifier may or may not be what you need.)

Update: Removed comments anent unavailability of documentation server.