Following each Census, each legislative body in Tennessee must redraw their districts so that each district has roughly the same population. This process is generally referred to as Redistricting.
The Election Commission plays no role in drawing the new district lines. Drawing the lines is strictly the responsibility of the Legislature, County Commission, and City Councils. Once those bodies have determined where their lines are, the Election Commission takes over and adjusts precinct lines as needed and notifies voters whose precincts have changed.