Obviously I don't know who trained you and what you covered, but if you have come away from the course not knowing what you need/what is available from the most obvious course to deliver, they haven't really done their job right. I would go back to your training provider and see what they recommend. If you are certificating through them, they might well have a say in what you need to do for their quality purposes.

Reading carefully, do you mean Emergency First Aid at Work? If so, you would need to be doing at least 6 First Aid at Work courses as well, or you would need to be approved by an Ofqual accredited awarding organisation. If it is the latter, they will probably have various assessment materials that you would need as well. If you have come away without knowing all this, I really don't think you have got your moneys worth.

If it is just Emergency First Aid, then no you can't give an HSE certificate.