Start by booting until the GRUB2 menu appears then edit the boot loader menu with the e key. Find the line beginning with linux and make then follow these steps.
- add rd.break
- run mount -o remount,rw /sysroot
- run chroot /sysroot
- run passwd
- run touch /.autorelabel
- exit chroot
- run mount -o remount,ro /sysroot
- exit resuce mode
Login with the password set in step 4 after rebooting.