To get rid of the bold letters
Go to the A= thingy that looks like this
Press on it and u should see a B with a blue square them that means BOLD IS ON. Press on it to make it go away.
It u only want to bold certain words then press bold finish typing the word then press on it again and it should return to normal wording again.

If it's ur phone keyboard that's effected and not just in the app then
High light all the words
Tap the arrow on the menu bar (OT appears with the words copy paste etc. But u wanna press the arrow)
Hit the B/U
And it should stop