alias alias_name="command_to_run"

alias l1="ls -1a"  

remove the alias

unalias 

bypass the alias : preceed alias with \ (backslach)

To make alias persistent, add into one of the various files that is read when a shell session begins.
Popular are ~/.bashrc and ~/.bash_profile

Restart your shell session in Linux (reprocess your initialization files)

To restart your shell session in Linux, use the source command to reprocess the user initialization files stored in your home directory.

Use source (or its shortcut . ) to reprocess the initialization files in your home directory:
source ~/.bash_profile
source ~/.bashrc
If .bash_profile is not present, reprocess .profile; enter: source ~/.profile