Hello audra237,
Thank you for using Apple Support Communities. Most likely, each device will have to set up Apple Music with Alexa in order to link to a specific speaker. This resource explains how to set that up: Play Apple Music with Alexa - Apple Support
Set up Apple Music with Alexa
1. Open the Amazon Alexa app.
2. In the lower-right corner, tap More.
3. Tap Skills & Games.
4. In the upper-right corner, tap the search field, then enter Apple Music.
5. Tap Enable To Use.
6. Tap Settings.
7. Tap Link Account.
8. Follow the instructions to sign in with your Apple ID. Get help signing in with two-factor authentication.
If a speaker is already set up with a different device, then unlink it:
Unlink Apple Music and Alexa
1. Open the Amazon Alexa app.
2. In the lower-right corner, tap More.
3. Tap Settings.
4. Scroll down and tap Music & Podcasts.
5. Under Services, tap Apple Music.
6. Tap Disable Skill.
For more help, reach out to Amazon Support: Alexa Features Help - Amazon Customer Service
Thank you for using Apple Support Communities. Take care.