To export the board, you can click on the top right menu icon and select export to Trello. When the export is completed, it is available with your boards in Trello.

Trello board needs to be in a workspace there. Hence, when you export a board, it's needed to select to which workspace it is going to be exported to:

You can disconnect the link between Trello and Placker by selecting the disconnect board option, this will remove the synchronization between the two boards completely, though they will remain disconnected in both places.

Another way to disconnect a board is from the board settings. You will have the option to keep it separate in Placker or also delete it there (the board will remain not synced in Trello):