The send button is located at the bottom of new emails or directly below the quick reply box. (You can find pointers here Where is the send button?)
Some people report that the send button is sometimes obscured by a toolbar or their taskbar settings.
If you are still unable to find the send button, could you kindly post (or DM) a screenshot of what you are seeing along with Operating System and Browser so I can investigate further.
Also, are you able to try on a different browser (Chrome, IE, Safari, Edge, Firefox, etc) and see if you have the same issues?
Thank you so much.