Hi Michelle Molnar,
Thanks for reaching out to Microsoft Q&A.
If you had taken a proper backup you can try restoring and it will automatically repopulate on your newly installed app. If not you have to add all your MFA accounts one by one.
Check the Common questions about the Microsoft Authenticator app
If none of these helps, I will suggest you to raise a support case with Microsoft(https://azure.microsoft.com/en-ca/support/create-ticket/).
Please Upvote and Accept as answer if the reply was helpful, this will be benefitting the other community members who go through the same issue.