Dampen a washcloth or a hand towel with white vinegar and set it on the marks.  The vinegar is supposed to "wake up" the dented carpet areas.  Or:

 

A friend of mine plugged in her steam iron and steamed the areas that were indented and it worked well for her.

 

 

 

adair

Adair- I'll try the vinegar, never have used that method. Thanks!!