How to type theta in mobile?

Excuse me, as a cryptocurrency and finance professional, I often encounter mathematical symbols in my work. However, I'm having a bit of trouble typing the Greek letter theta on my mobile device. Could you please guide me on how to accomplish this task? It's crucial for me to accurately represent certain equations and notations in my correspondence. Thank you for your assistance in this matter, as I believe it will enhance my ability to communicate effectively within my field.