Touch the tip or front edge of your tongue to the roof of your mouth just behind your teeth. Keep your jaw relaxed. Stop the air, then release with a puff.

Americans pronounce toothache as TOOTH-ayk (/ˈtuθˌeɪk/). Stress falls on the first syllable — keep everything else short and quick. You'll hear it in sentences like "Arthur had a toothache in his mouth south".
Record yourself saying "toothache" 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.
Touch the tip or front edge of your tongue to the roof of your mouth just behind your teeth. Keep your jaw relaxed. Stop the air, then release with a puff.

Round your lips into a tight circle. Let your tongue rest in the middle of your mouth, slightly raised.
Place the very tip of your tongue slightly between your teeth. Blow air gently around it without voicing.

The textbook way isn't wrong — it's just not how anyone actually says it.
Stress falls on the first syllable, not the others. Stretch TOOTH — keep everything else short and quick.