Send button in Thunderbird for Android

I have used Thunderbird on my desktop PC for many years, and have now installed it on a Lenovo tablet running Android. The setting up was simple (thank you), and I am receiving emails with no problem. I have tried sending emails and they are simple to type up, but there is no visible "Send" button. I have accidentally sent an email successfully, but have no idea of how this came about. Please help me to send emails, as I am very keen to use the tablet fully. Many thanks, Nigel Olliver.