Singular subject followed by verb without "s"

This is the sentence I wish to construct:

When the show finishes, someone remind the ice-cream man to start
picking up the garbage.

The verb in question is "remind". Should it be "remind" or "reminds"?

I have a hunch that it should be "remind". If so, why is the subject and verb not in agreement? (Normally "someone reminds" is considered correct.)

Is there a grammatical term to describe this type of usage? Any reference would be helpful too.

Thanks