Hi Denise,
They are tiny and straw colored disks so they are difficult to see. When the blooms become old dry tiny paper lantern type things, Pop them off into a bag. I did find some flowers never fertilized and then there was just a shrived flower on them. If you are not sure if they are ready to pick, just pick a few. Then bring them inside and pull them apart on a plate or sheet of paper. You should be able to see them then. If you see tiny white or green disks, you are picking them too soon.
Remy

Agree. I wait until the flowers are brown, crispy.

Then I cut the spent flowers and put them into a ziploc.

I leave the ziploc bag open to the air for several months.

Then I just seal the bag and shake it.

Torenia gives TONS of seed.
Q