General Information:

Here the he words "he," "him," and "his" refer to Apollos. (See: Acts 18:24-26)

Achaia was a Roman Province in the southern section of Greece. See how you translated this in Acts 18:12.

to pass over into Achaia

"to go to the region of Achaia." The phrase "pass over" is used here because Apollos had to cross the Aegean Sea to get to Achaia from Ephesus.

The word "brothers" here refers to men and women believers. You can make explicit that these are believers in Ephesus. AT: "fellow believers in Ephesus" (See: rc://en/ta/man/translate/figs-gendernotations and rc://en/ta/man/translate/figs-explicit)

"wrote a letter to the Christians in Achaia"

"those who had believed in salvation by grace" or "those who by God's grace believed in Jesus"

"In public debate Apollos powerfully showed that the Jews were wrong"

"as he showed them by the scriptures that Jesus is the Christ"