Well you need to get rid of that repeating field and replace it with a related table.
You have a many to many relationship between staff and jobs. A staff member can be assigned to many jobs and a job can be linked to many staff members.
Start with these relationships:
Staff::__pkStaffID = Staff_Job::_fkStaffID
Job::__pkJobID = Staff_Job::_fkJobID
You can place a portal to Staff_Job on the Staff layout to list and select a Job record for each given Staff record. Fields from Job can be included in the Portal to show additional info about each selected Job record and the _fkJobID field can be set up with a value list for selecting Job records by their ID field. The same basic approach can be used with a Job layout to list staff assigned to that job.
For an explanation of the notation that I am using, see the first post of: Common Forum Relationship and Field Notations Explained
Thank you for taking the time to reply. In fact, I have got it working exactly as I wanted it to... with the repeating fields still in place.
I changed the Pop Up to bring over the Key Field (called Staff ID) as the first value and the combined First/Last field as the second. I ticked the box to show only the second value. I then created a new repeating field and set it equal to the corresponding Pop Up value. This gave me the relevant Staff ID against each name in order for the Portal on the Staff page to work.