Follow below steps to reset redhat/fedora directory manager password.
1. /etc/init.d/dirsrv stop
2. Generate new password with pwdhash command. (pwdhash <new password>
3. cd /etc/dirsrv/slapd-instance name
4. vi dse.ldif
5. Replace value of nsslapd-rootpw variable to new generated password.
6. Save that file
7. /etc/init.d/dirsrv start
Note: Take Backup of dse.ldif file before modifying.