Hi, based on the document checklist, your immediate supervisor can attest to your experience. It does not have to be an HR personnel. Here is the instruction from the website.
For each job declared in the Application for Selection Certificate: •Work certificate or attestation Each work certificate or attestation must contain the following elements:
–The exact period of your employment at the company
–The number of hours worked per week
–The positions that you have held and the period during which you held each position
–The principal tasks and duties of each position
–The signature of your immediate supervisor or the company's personnel representative along with his name written in block letters
–The date of the signature.