Hi, Hayra.Valecha,
If you don't have the option when using the web app, can you possibly try using the mobile app to leave the team you're a part of for testing purposes?
If you still don't have the option, you would need to ask the IT admin of the organization to remove you.
May I confirm though, are you a guest user of the organization? If yes, and you want to leave it, you may sign in to My Apps (microsoft.com), and click on your profile photo > Switch organization to make sure you are signed in with the one you want to be removed. Otherwise, select the correct one.
Then, on the top left corner, click the downward caret beside My Apps > My Account > Organizations, Manage Organizations. Then, select the org and leave.
However, if it is your home organization, you will see a message that you won't be able to leave it, so you would need to ask your admin to remove you.
Looking forward to your response.