Just like the first island, there were no guidelines on the fifth.
The only information these future Supremes learned was that they needed to purify their Nonexistence. Other than that, they were on their own.
So, from Damien's perspective, what needed to be done to achieve that level of purification?
'I really don't know.'
Purifying Nonexistence wasn't necessarily a thing that could be done. It took whatever form it took based on one's experiences. Damien's Nonexistence was pure because he'd never polluted it in the first place.
But, for those who made it this far with a polluted concept, the situation was different.
They had to establish methods to purify Nonexistence before attempting it.