Open Termux App (Download Latest from F-Droid) , copy below link and paste in termux app.
apt update -y && apt upgrade -y && pkg install git -y && git clone https://github.com/Bhai4You/Termux-Banner && cd Termux-Banner && bash requirement.sh && bash t-ban.sh
here enter banner name and cowsay name for your banner like below screenshot.
successfully installed termux banner ! restart your termux app to see effect of termux banner !
for remove or back to default termux you need to type below command in termux. make sure you are in Termux-Banner Directory.
bash remove.sh