Full screen toggle button just below the iframe

I am using the Astra theme and publishing some games on this site on WordPress.

I have obtained the license of games and use embed codes to publish them on my site. However, want to add a full-screen toggle button just below the iframe so that if someone wishes to play the game in full-screen mode then he can just hit the button, same as this website offers a full-screen button to the bottom of the game iframe – visit the sample page here.

Can you please help me with this?