Hi
If you go into the online membership form you get the option to apply for full membership or the affiliate certificate.
For full membership, you have to provide the details of the person/people who can confirm you have met the experience requirements (i.e. your STR supervisor or PER mentor). You then have to send these people the blank reference form,m which they can either send back to you to send on to ACCA, or they can send it direct to ACCA themselves.
There is a part in the FAQ section on what to do if you have lost touch with one of your potential referees.
I hope this helps. I submitted mine on Tuesday, and I’m now collating my references (4! due to changing jobs and my previous line manager moving jobs himself!)