In the Backoffice, open the Critical Path section and locate the critical path you want to copy. Click the copy icon (two stacked sheets) next to the critical path to create a duplicate that you can then modify.
If you cannot copy a critical path to a specific airport, you may not have the required permissions. Contact your administrator to request access to the target airport.
If no one in your organization has access to that airport, please contact Tarmac support through your usual channel.