en_tn_lite_do_not_use/act/13/31.md

He was seen for many days by those who had come up with him ... Jerusalem

This can be stated in active form. Alternate translation: "The disciples who traveled with Jesus ... Jeruaslem saw him for many days" (See: rc://en/ta/man/translate/figs-activepassive)

many days

We know from other writings that this period was 40 days. Translate "many days" with a term that would be appropriate for that length of time.

are now his witnesses to the people

"are now testifying to the people about Jesus" or "are now telling the people about Jesus"