To begin, tap on the "Settings" icon, which looks like a gear, and then select "Privacy and Security". From there, you'll see an option to delete your account, which is clearly labeled. This is where you'll start the process of permanently removing your Telegram account.
When you choose to delete your account, Telegram will ask for your phone number to confirm that you're the account owner. This is a security measure to ensure that your account isn't deleted by someone else. After you enter your phone number, you'll receive a code to confirm the deletion.
