I forgive, I was not clearly!!
I am mentioning itself, to the small boat, where it has a key.
With this necessary key to open an iron door, but I do not find the
keyhole...I am to a step to find me with Sophia.
Sorry, I totally misunderstood where you are. I thought you are on the ship in Palawan Lagoon - overlooked the topic title which says "Palawan Volcano". Shame on me
The keyhole is behind that grated gate (the iron door you're talking about). You must open this first. To do so, dive into the hole on the ground of the pool just in front of the grated gate. Follow that way - and solve the puzzle which awaits you there
I don't want to make it too easy.
Ok so you now you have dived into the hole on the bottom of the pool just in front of the grated gate. My hint is to swim slowly and look above you - you will see what you need to progress further.