Hi Tabbykat403,
welcome to the Apple (user-to-user) Community!
Re: Can’t pass fit test to use as hearing aid
Wondering if Apple support's online articles (links below)may help with the fit.
ie: Some tiny adjustment may make all the difference!
If you haven't already tried following Apple's suggestions:
See: Choose your AirPods Pro ear tips and use the Ear Tip Fit Test - Apple Support
and
How to: Get the right fit with AirPods 3 or AirPods Pro - Apple Support
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More support / info. if needed:
AirPods Support Website:
Find all the topics, resources, and contact options you need for your AirPods...
AirPods Support - Official Apple Support
All the best :-)