Place your tongue tip near the roof of your mouth behind your top teeth. Push air through the narrow gap. No voicing.

Americans pronounce seafood as SEE-food (/ˈsiˌfud/). Stress falls on the first syllable — keep everything else short and quick. You'll hear it in sentences like "We had amazing seafood for dinner last night".
Record yourself saying "seafood" and play it back. The mic stays on your device — nothing's uploaded.
2 syllables, 5 sounds. Tap a syllable to jump to its row, then explore each sound's mouth shape and how it's made.
Lift your bottom lip to touch the very bottom of your top front teeth. Blow air through this contact point without voicing.

Round your lips into a tight circle. Let your tongue rest in the middle of your mouth, slightly raised.
Touch the tip of your tongue to the roof of your mouth just behind your teeth. Add vocal cord vibration as you release.

The textbook way isn't wrong — it's just not how anyone actually says it.
In "seafood", the "d" is not released — the articulators get into position but hold without the burst of air. Air stops but there's no release burst — the articulators hold position.
Stress falls on the first syllable, not the others. Stretch SEE — keep everything else short and quick.