To help with something. A noun or pronoun can be used between "assist" and "in." Who wants to assist me in this endeavor? My boss wants me to assist in this project, so here I am!
assist someone in something
to help a particular person working on a task. Please assist Greg in the committee's assignment. We assisted him in the whole procedure.
assist in something
to help with something. May I assist in this? Please assist in this task.