First off, changing the date format won't change 3/1/2021 to any February date: it's either the 3rd of January, or the 1st March.
And if it's this row you are talking about then it's trivial:
dtLicenceAvgData.Rows[0]["Period"] = Convert.ToDateTime(dtLicenceAvgData.Rows[0]["Period"]).ToString("mm-dd-yyyy");
Just change the format string you specify in the ToString call to
"dd-MMM-yyyy hh:mm tt"
Do note the case is important here, and your original code is wrong: "mm" does not select months, it selects minutes. "MM" is months as a number.
This may help:
Formatting a DateTime for display - format string description[
^]