Execute the below commands in termux app

1) pkg update

2) pkg upgrade

3) git clone https://github.com/Bhai4You/Termux-Banner.git

4) ls

5) cd Termux-Banner

6) ls

7) chmod +x requirement.sh

8) ls

9) chmod +x t-ban.sh

10) ls

11) bash requirements.sh

12) bash t-ban.sh

After executing this command it will take 2 minutes to download the tool
After that it will ask enter your banner name and enter your cowsay name after
The entering both name press the enter then open new terminal