"Those books were not here yesterday."
Translation:Ty knihy tady včera nebyly.
It must be knihy, not knihi, because h is a hard consonant, it always must have y.
The word order also sounds unnatural. "Ty knihy tady včera nebyly." is much better. Tady probably prefers to be in the second position (if it is not first or last) because "Včera tady nebyly." is fine.