(ja)
mýlím se
I am mistaken
(ty)
mýlíš se
You (informal, singular) are mistaken
(on,ona)
mýlí se
He / She / It is mistaken
(my)
mýlíme se
We are mistaken
(vy)
mýlíte se
You (formal / plural) are mistaken
(oni)
mýlí se or myslejí
They are mistaken