1. Click Analysis > Information Library
  2. Click Add an ad-hoc query
  3. Choose Constituents as the Source View
  4. In the left column, select Constituent
  5. From the middle column, underneath System Fields drag Changed by username to Include records where
  6. From the middle column, underneath System Fields drag Date Changed to Results fields to display
  7. From the middle column, underneath Fields drag Lookup ID, First Name and Last name to Results fields to display.
  8. Add additional fields to Results Fields to Display. This can vary based off of what information you would like to see in the results.
  9. Save the query

Below is an example of what your query should look like:
Query on Changes to Record by Application User