The word "collected" IS used in this context, to bring together in a group. "The teacher collected the students from the various exhibits at the museum and led them to the bus."
"I can help you with various concerns, please let me know." is a comma-splice. Use a semicolon, a period, a conjunction or a begin the sentence with "If".
As you can see, policing grammar on a forum or blog is pedantic and presumptuous, especially for an oxymoronic "native English speaker from the USA".