Is it possible to edit a project that is already created and for example adding a competency profile?

It is not possible to edit a project that is already created. Close this project and erase it and then create a new project. If the candidates have already completed the test/tests, then follow the instructions in the article on how to add the candidates in the new project and transfer their scores into the new project: How do I transfer in a candidate’s previous test score into a new project?