Navigate to the project's project tasks and click Mass Link Project Task Assignments.
On the Mass Link Project Task Assignments with a Resource Request and an Assignment page, select the project whose project task assignments you want to link.
Click Filter. The project task assignments that meet your criteria are displayed.
Select the project task assignments you want to link.
In the Assignment and Resource Request Selection Panel, from the lookups select the Resource Request or the Assignment or both you want to link the assignments to.
Click Link. PSA links the project tasks assignments to the selected resource request, assignment or both.