For some reason I can't find FES on the app.
EDIT: Nevermind, found it, but I'm starting to get annoyed by this app more with each passing moment. It won't let me sign in to the forum. It says "Snupes" doesn't exist, but then when I try to sign in under "Supertails" it says my password is incorrect (I assure you it is not; even reset it for good measure).
I wouldn't judge just based on your difficulties logging in.
I'm not sure what could be the problem for you but I prefer to use social logins for things because I don't like making accounts for everything on the internet. With that in mind, you can make a Tapatalk account with G+ or Facebook and when you do then all your forums that have Tapatalk enabled will verify that you are you automatically. When I clicked the link from the email this morning, the app opened and offered to subscribe me to tfes but it didn't prompt me to input my username or password because Tapatalk already knew who I was, probably because of my email address, which tapatalk knows is associated with a user named rottingroom for this particular forum.
For things on my phone where I do have to input a password, I don't bother at all with manually inputting them because I am a lastpass user. I don't actually know any of my passwords.
Hope you can sort it out though. If you simply can't remember your password you might be able to open your security settings on Chrome for the desktop to see your stored passwords.