Have you looked at the various Alexa Skills for spelling? There are dozens and dozens of free spelling-related Skills. Here are a few:

https://www.amazon.com/Alex-H-To-Spelling-Squad/dp/B079HGLLGM

https://www.amazon.com/Self-Spell-Bowl/dp/B08JLWRF85

https://www.amazon.com/midnight-wrench-letters-to-word/dp/B01EMTFKEU

https://www.amazon.com/ankur-karoliwal-spell-out/dp/B077Y2ZLYF