There are two ways of updating Existing Work History in Mercury. You could re-send the Candidate's updated CV to your Mercury CV email address, that would re-parse the CV and would attach a new document version to the Candidate's record.
You could also update the Work History fields manually or add a New Work History.
Click Contacts > find the Contact record you wish to update > Click on the Contact's name > Click Experience > Put a check-mark next to the position you'd like to update > Click Edit
Update the fields necessary > Click Save and Close
In this example the End Date was updated. Remember to Click Save or Save & Close if you are finished.
You can also + New Work History if you need to add a new job.
Complete the required fields and click Save and Close
The new Work History will be shown at the top if it was set at the Latest position, if not, then jobs will appear in chronological order. Click Save & Close if you are finished.