Please follow the steps below to filter a data range to have values below the average, or check to filter a data range to have values above average.
Step 1: Select the row you want to filter on, normally the top header row;
Step 2: Click the "Home" tab from the ribbon;
Step 3: Click "Sort & Filter" and select "Filter" from the drop-down list;
Step 4: You will find the small triangles are added to the selected row;
Step 5: Click the small triangle in a column (e.g., column C - Salary) and click "Number Filters", select "Below Average".