How do I make a new tour with new and existing stops combined?

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Go to the Toureditor > click add tour, fill in the name of your new tour and choose the language(s) >
Open your new tour > click add stop > choose select existing and make your choice. (You can add more than one stop by clicking the square in front of the stops).

When you have selected all the stops you want to keep in your new tour, you can start adding the new stops. When you are finished disconnect the start Identifiers from the old tour and add them to your new tour. Do not forget to publish and synchronize. Then move your old tour to Archive by clicking the square in front of the old tour > actions > remove > archive. (This way all the analytics of the old tour will be saved and the old tour is still visible in MapMyVisit).