If you go to the Flow Details Page, and you look at Connections (there should be one for Exchange/Office365).
That one I am guessing is running only as Dev? Can you please check. You maybe able to simply create a New Connection (which can be done within the Flow itself, by clicking ... and selecting to create a new one) and make the Test Account the sign for it.
If that works then you should be golden as the connection is what matters.
However, as for creating a new flow, my understanding is from our post, these are both service accounts. So you would either essentially add the additional service account as the owner, then remove the original, or you would have to create a new one and just make sure you assign the service account as the owner
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Michael Gernaey MCT | MCSE | MCP | Self-Contractor| Ex-Microsoft
https://gernaeysoftware.com
LinkedIn: https://www.linkedin.com/in/michaelgernaey