If a project has been deleted, automatic assignment is not possible. You can recognize this by the corresponding icon in the directory tree. In the left-hand table of the old project, the icon is displayed on each line. The right-hand table of the new project is missing.

If it is fact that this project does not exist anymore, then confirm the missing assignment.

Missing assignment confirmed

Click on the Confirm all assignments [Verify all mappings] button.

All assignments confirmed: The respective icons are shown in the directory tree and in the table.

In a similar case, you may want to assign a different project manually. You can find a description of manual assignment at Section 6.10.2.3.1, “Plus button” -> Add target project.