As we know, Ezra the Scribe changed the Hebrew script to Assyrian script. How do we know he also didn’t change the content of the verses? Thanks in advance.
Your question is perplexing. Ezra did not translate the Torah into another language, but merely changed the shape of the letters. Everyone continued to read the Torah in the same way as before.
Also keep in mind Ezra lived in the period concluding the exile, after the entire 24 books of the Bible had already been composed, all of which had been passed down over the years by tradition and were well known to the people.
It says explicitly that in his period there were judges and priests, and without a doubt they knew the Torah — even if the masses did not precisely fulfill the Torah. (Their situation can be compared today to the majority of Israelis who do not know that it is forbidden to shave with a razor, despite it being a explicit commandment in the Torah. But they know about circumcision and tzitzit and tefillin and mezuzah and Shabbat, who was Moses, etc.).
Secondly, centuries before Ezra, there were already a group of Samaritans, who have survived down until today, and they also transmitted the Torah separately.