Can you substitute coriander seeds for fresh coriander?

Yes, just reduce the amount you use.

Coriander actually comes from a cilantro plant that goes to seed. Commercial coriander comes from cilantro plants that are breed to seed more quickly and abundantly.

Coriander is an herb that has two primary forms: leaves and fruit. The leaves are typically sold as an herb called cilantro in the United States and the fruit is typically sold as whole coriander...

Use 1 tbsp dried coriander for 3 tbsp freshly chopped.

Not if you want it to taste the same! The leaf of the same plant is cilantro.