Make the value for END_DATE in FND_USER null, of course.
SQL>SET END_DATE = ''
SQL>WHERE USER_NAME = '[Your User Name]';
To do it in Perl just use the code I’ve got below (in mod_ebsdb) and substitute the above SQL for the value of $sql (you might want to change what you print to console in order to prevent confusion). Like this:
my $sql= "UPDATE FND_USER
SET END_DATE = ''
WHERE USER_NAME = '$user_name'";
The aforementioned code will commit the transaction, assuming it passes the simple “Does this USER_NAME exist?” test.