Pending salary lines will show on an employee's profile in their Pay History page. To view them and approve or reject:
Search for the employee and go to their profile.
Click Payroll, then Pay.
Click Pay History and select the relevant pending line.
Click Approve or Reject.
If rejecting a line doesn't remove it from Pay History, try rejecting it from the negotiating body:
Go to Setup and click Settings.
Click Payroll Settings, then Pay Grade and Payscale.
Click the arrow icon on the negotiating body the employee is on.
Click the Salary Changes tab.
Find the employee in the list and click them.
Click Reject Pay Change.