Do you want to push the row into your MailChimp list when a new row is added in your Excel sheet?
Thanks for your feedback, the "When a new row is added" trigger is not supported in Excel connector or Excel Online (OneDrive) connector of Microsoft Flow currently, I afraid that there is no way to achieve your needs in Microsoft Flow currently.
If you would like this feature to be added in Microsoft Flow, please submit an idea to Flow Ideas Forum:
Thank you for posting to the Flow Forum! Our team is dedicated to creating a positive product experience and value your insight on how we can improve our product features.
As @v-xida-msft mentioned, although there currently is no Flow feature addressing your need of "When a new row is added" trigger in Excel connector or Excel Online (OneDrive) connector at the moment, we highly encourage you to submit your feature idea to the Flow Ideas Form!
Once you've submitted your idea to the Flow Ideas Forum, we'd love to follow its voting progress.
Please respond below with the link to your idea in the Flow Ideas Forum and mark it as an "Accepted Solution" so other community members may track its progress and help amplify its value with their votes in the Ideas Forum.
The more other community members view and vote on your idea, it will increase its visibility and prioritization to our Product Development team who moderates the Ideas Forum.
Should your idea become a reality as an improved Flow feature, we will link the solution back to this thread for reference.
-AT (Flow Community Admin)