Yes, it is possible to remove candidates from an ongoing selection process, but only if it does not have test instances created. To do so, you must:
On the Evalart home page, select the option "Selection Processes", located on the top menu.
Click on "Processes list".
When you enter the process list, click on the key icon located to the right of the process you want to modify.
When accessing the configuration menu, in the "Candidates" section, click on the "Options" button, located to the right of the candidate you wish to delete. The candidate is removed from the process, but not from the candidate database.
Click on "Delete".