How do I add/adjust words in/to the keyboard dictionary on iOS?
Go to Setttings > General > Keyboard.
Tap Edit in the top right corner.
Tap Add New Shortcut. Type the word you wanted to add to the dictionary in the Phrase field. You can also optionally add a shortcut.
Add a shortcut with the Phrase TE and the shortcut te. This will auto-capitalise te to TE. It will also prevent it from auto-correcting to the.