Within the Data Display window, there are a number of ways you can search for particular data.
You can do a "simple" find - this scans the grid for a particular string. You can do this by clicking on the Find button, or with Edit > Find (or Ctrl+F). There are three options for finding rows:
In the case of the second two options, you can re-show all rows with Ctrl+F > UnHide all rows. The row-hide / highlight will also be reset when you refresh the data.
Note that this function just scans the data that is displayed in the grid. If you aren't displaying all the table, there may be rows in the table that aren't found by this function.
Another options is to use Search Table (see Tools > Search Table or the Search icon). This provides a simple dialog for building simple searches against your table.
Unlike the Find, this will run a query against the database so that all rows that meet the specified condition are returned.
If you wish to build more complex searches, click on the SQL or Query Builder icons.
Another quick way to build a search is to right-click a value in the grid and select either Only show rows with this value or Exclude rows with this value. AQT will build a query to display or exclude those rows from the table.
You can select Only show rows with this value (another condition) to add this search condition to your existing search conditions.
If you want to re-show the entire table, right-click and select Display entire table.