Make sure you got correct project role, any role where capture is set to ‘view’ will not be able to perform this action. If you are a SCRUM master then you should be able to perform this by default else contact your SCRUM master to get appropriate role where Capture is set to ‘Edit’.
Hope this helps!
Please find my screen shot below when trying to edit Business Engineer role.
I am with the role of Scrum Master.