Where did Apollos minister after being instructed by Priscilla and Aquila, and what was he doing there?

After Priscilla and Aquila expounded the way of God more accurately, Apollos publicly convinced the Jews from the Scriptures that Jesus was the Christ. Later, the same man was at the congregation in Corinth, holding forth with eloquence and a capability of opening the Scriptures.

Les explains that after Paul's departure, Priscilla and Aquila did not forget what they heard. When Apollos knew only John's baptism, they likely took him home, and across the dinner table they unloaded on that eloquent man. Then in Acts 18:28 he mightily convinced the Jews publicly, showing by the Scriptures that Jesus was the Christ. Later, the same man followed in Paul's footsteps and was at the congregation in Corinth, holding forth with eloquence and ability to open the Scriptures.

1 Corinthians 3

What was Apollos doing in Corinth when Paul wrote 1 Corinthians?

Apollos was at the congregation in Corinth, holding forth with eloquence and a capability of opening the Scriptures. He had followed in Paul's footsteps and was actively ministering there when Paul wrote 1 Corinthians. He was not merely present but was engaged in eloquent proclamation and Scriptural exposition.