step into
step into {v.}
1. To come or go into.
The taxi stopped, and we stepped into it.
Mr. Jones called to his secretary to step into his office.
2. To begin to do, undertake.
When the star became sick, his understudy stepped into his part.
When Bill graduates from college, he will step into a job in his father's bank.
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Source: A Dictionary of American Idioms