Hello mate
Not familiar with IAA regulations but a quick look at Form 19 directed to PLAMs.
In particular PLAMs 020, 021 and 032.
Looks like IAA issue a log book, which I assume will be similar to the CAP 741 logbook.
This could be used to support you Form 19 application.
It should have instructions like CAP 741. As per the CAP 741 there is guidance on who can oversign your tasks. They should be able to advise how to complete all the required documents.