In order to use this theme you need to put it in the .oh-my-bash directory.
Once slickwit theme is in the .oh-my-bash/themes directory then you can change your theme in the .bashrc file.
# Path to your oh-my-bash installation.
export OSH='/.oh-my-bash'
OSH_THEME="slickwit" # folder name of the theme
source "$OSH"/oh-my-bash.sh