Click on the property set that you would like to assign access to. 

Navigate to the right hand side and click on the unassigned dropdown window.

Type in the name of the external organisation that you would like to assign project access to. A dropdown will appear providing you with options to confirm your selection.

Press on the assign organisation button once you have found the organisation that you are looking for. Well done! You have now assigned the property set to the external organisation. 

Providing External Organisations Access To Your Project