Involve oneself or intervene, as in He knew he'd be able to step into a job in his father's firm, or Jane asked Mary to step into the matter and settle it. Also see step in.
Words nearby step into
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.