To share a Miro board, open the board and take both of the following steps:
Go to Share and type in the email addresses of the people you want to share the board with and add them as Commenters. This will provide them only with the ability to comment and to be tagged, not to edit.
Further down, look for Anyone With the Link and change this to Can Edit. This will allow them to make edits and co-create on the board.
Once this setting is changed, copy the board link and share it with anyone who needs access.
Watch this video tutorial for more details.