I found that it’s not possible in the first version.
https://community.miro.com/product-news-31/diagram-as-code-plantuml-and-mermaid-js-9691?postid=40399#post40399

Hi @Yasushi SHOJI ,

We’ve made a few updates to Mermaid. You can now edit your diagrams, to edit, select the image generated by one of the apps and then click the toolbar icon. The source of the original diagram will be loaded in the editor.

Here you can find all the updates we made.

Best,

Turner 

Which icon are you talking about for editing?
 

Ah! This? that’s not intuitive is it?  But once I know I can work with it.

Thanks for your update!

This stopped working not too long ago - anyone else having this issue?

Having the same issue.

When Mermaid diagram was added by the plugin, it is added as an image and it is not possible to re-open as Mermaid code.

Following steps described above, click on the diagram and then on the Mermaid button in the sidebar, it opens Mermaid editor with blank code. There is no way for me to retrieve the code once added. It is like burning to CD-ROM.

It would be nice to have an option to convert this to a Miro Diagram to allow it to be editable directly in Miro

Same problem - appears to happen with larger diagrams, be great to get this fixed.

I just tried it with one of the small sample diagrams and same problem -- editor opens with no code.