How? Installing the right tools and changing configuration files wich are typically (but not always) located under /home/[your user]/.config/[application]

For example neofetch config is located at ~/.config/neofetch/config But i think that's not the default config. An example config would be typically (but again not always) located at /usr/share/[application)

So what you would do is

cp -r /usr/share/neofetch ~/.config

vim ~/.config/neofetch/config

And edit the file however you want. Syntax is rarely the same between apps so prepare documentation if you do more than just change values

(Replace vim with you editor of choice)