From Fedora Project Wiki
1. At the Kernel selection line, press [E] while highlighting the latest working Kernel.
2. Using the arrow keys, move the cursor down to the line beginning with "linux".
3. Press [END].
4. Press [SPACEBAR].
5. Place 'rd.break' at the end of the line.
6. Press [CTRL]+[X].
7. At the "switch_root" prompt, execute the following command:
# mount -o remount,rw /sysroot
8. Execute the following command:
# chroot /sysroot
9. Provide a new root password by executing the following command:
# passwd
10. Enable an automatic fcontext relabel with the following command:
# touch /.autorelabel
11. Press [CTRL]+[D].
12. Execute the following command:
# reboot