Reset Siri's Training Data to Force It to Relearn Your Voice

Siri does a pretty good job of learning your voice and dialect so it understands you.

All you oughta do is turn Siri off and back on again.

Head to prefs > General > Siri and toggle the Siri option to Off.

Then, head to tweaks > General > Keyboards and turn off Enable Dictation.

iOS: Deleting Siris Training Data| Mac Observer