There will be a force routing for that particular pin. In order to remove that particular pin from force routing, please go to "Design Wide Resources" in the PSoC Creator and select "Directives" and Remove the Directives which are available in the section.
Please let me know if this helps.
Please search for a file of extension .ctl in your workspace explorer.
You have to edit the current file. Please check the control file section in the following document to see the format.