Work permit extension (Harare)

Hi there,
I understand the following is required for an extension of a TEP:
1. Letter of application
2. Copy of expiring TEP
3. Details of person doing understudy on letterhead of company including contact details

Could anyone shed some light on what no. 3 means ("person doing understudy on letterhead of company"). Is that the applicant? Or the employer?
Otherwise I would add my CV and qualifications.
Anything else needed?
A lot of you will have undergone this procedure at some stage.
Looking forward to hearing your advice.
Thanks,
Ute