Edit the Boot Entry: Use the arrow keys to highlight the default boot entry (usually the latest kernel) and press the e key to edit the boot parameters.
Modify the Kernel Line: Locate the line starting with linux or linux16. This line contains the kernel boot parameters. 
Replace the ro (read-only) flag with rw (read-write) to allow write access to the root filesystem.
Then, append one of the following options to the end of this line:
- single or 1 to boot into single-user mode.
- systemd.unit=rescue.target to boot into rescue mode, which is the modern systemd equivalent of single-user mode.
- systemd.unit=emergency.target for emergency mode, which provides a minimal environment with the root filesystem not mounted.

init=/bin/bash to directly start a bash shell as the init process, bypassing the normal init system.
Boot the System: Press Ctrl+X or F10 to boot the system with the modified parameters.