To Edit Pension Scheme Assigned to Individual Employee's, go to the Pension big button at the top in the Tasking zone. Please follow the below Road Map:

Road Map - To Edit Pension Scheme Assigned to Individual Employee's.
Pension -> Group Assigning -> Click the Link Assign Pension Scheme (individual) -> Click the Edit button under scheme detail -> Click on Save button.
('Pension' is the button positioned in the tasking zone menu at the top. It is the third button from the Right)