Use the link below. When the page loads, you want to request desktop site in your tools menu. This will give you the same browser as you would have on laptop/desktop computer. Then enter your email address you used to sign up in "Trainer mode" and enter your birthday. Don't need to input anything else. Just click recover username. An email will be sent with link to click.

Use this link:

https://club.pokemon.com/us/pokemon-trainer-club/forgot-username

When the page loads, you want to request desktop site in your tools menu. This will give you the same browser as you would have on laptop/desktop computer. Then enter your email address you used to sign up in "Trainer mode" and enter your birthday. Don't need to input anything else. In the email that will be sent, just click the green box "recover username".