Find the EGR valve on the intake manifold and trace the vacuum hose
from the diaphragm to the EGR solenoid.  It should have a two-wire
electrical connector on it and another vacuum line going to the
throttle body, intake or vacuum manifold.  The EGR solenoid opens up at
cruising speeds to allow vacuum to pull the EGR diaphragm in, to allow
the exhaust gasses to get recycled into the combustion chamber.

You can connect some test leads from the EGR solenoid to the battery
terminals to see if it pulls in ("clicks") when voltage is applied.  A
vacuum pump will tell you if it holds vacuum on the intake source side
without voltage applied and if it releases the vacuum when voltage is
applied.

That's how I've tested them on other Fords, never worked on an Aspire.
Assuming same setup.