I installed the Scenery Consid Editor and when I opened it up I found every scenery had a red triangle next to it. What is the best way to fix this?

Thank you in advance.

From the manual:

"Finally, Areas are automatically checked for a number of possible errors. If there are any errors,
this will get shown to you by a red cross in the information section below the buttons. Should an
area have an error, a red warning triangle will appear in the column which where there is a problem,
and information explaining the error will be placed in the Errors column. The main errors that get
shown like this include: Areas which have non-unique titles, (Triangle appears in the title column),
Areas which have non-unique paths, (Triangle appears in the path column), and if you have the check
scenery directories exist option set, Areas where the directory the path relates to cannot be found.
(Triangle appears in the path column.)
If you wish to find the areas which have errors quickly, you can scroll across to the Errors column and
click it. This will re-sort the table and move them to the top. (Clicking it a second time will send them
to the bottom.) You can also click the red cross icon in the information section, this will select all the
areas that have errors.
Remember: No action is saved until you save using the CTRL-S or choose the save option of the file
menu. If you are editing the default scenery scenery.cfg this save action will save as NewScenery.cfg
rather than scenery.cfg."

Worse case scenario, you could save the scenery.cfg file as a backup, then delete it from its current location.  Starting FSX will create a new one with the default scenery.  You would then use Scenery Config Editor to add your add-on scenery.  

Thank you for the trouble of helping me.

No trouble at all.  Hope it helped.