The VR tour you already created can be modified at any time. Just hit the “Edit” button in the tour options to apply changes to it. You will be taken back to the tour creation panel.
You can access this option while logged in, as shown below:
If you can’t see such option, it’s probably because the tour is in the “Released” state. This can be reversed - upon clicking "released" again, you will be able to edit your tour again.
Important note: Magic Links and Magic Codes will remain the same upon applying changes to the tour in the editing mode, so no worries - your client will not lose access to it if you want to adjust some details. The link will change, however, when you release the tour (or un-release it) so keep that in mind for the Shared Experience feature.