How do I unlock perplexing pool And how do I find the yelow pikmin?

Well you are going to need to get the other part of the globe, which is in the forest in awakening wood.
GO into the forest and explore around a bit but you are going to need a lot of pikmin.......lets say 56 (Possible) because there are a lot of monsters in there so just keep on getting flowers and get some purple pikmin too. You're going to need them. Trust me.

And Then When you found it. The yellow pikmin are in perplexing pool. Keep walking with your red and purple pikmin (kill enemies along the way) And then you will come across two blocks.(DO NOT GO INTO THE WATER OR ELSE YOUR PIKMIN WILL DROWN)
What you have to do with these is put your red pikmin with you and then throw your purple pikmin onto the opposite block. 1 Purple pikmin = 10 red pikmin.

It will take a few tries but you will eventually get up. On the top use your red pikmin only and watch out for the flyying thing the picks your pikmin up and slams it down underground.
You will see a BIG red Bulborb on fire. Red pikmin will kill that but do not waste time to drag him back to the onion. There you will see a poison gate. Get white pikmin if you haven't already. 15 should let you break it down quickly. Once you have....

VICTORY!!!!!!!
Yellow Pikmin Are Yours!!!
Hope this was helpful.

To unlock the place find the mapp in the secound place, and for yellows, go around the left of the tree, there should be a path, go up it and defeat some enememys with them, then their yours

You must go to awakening woods then try to find the second half of the map.then you should unlock perplex pool. Then pause the game and look around the map and look for a yellow onion and look for a path to the yellow pikmin in the tree then sneak past the flaming bulborb and use the white pikmin to breakthe poisen wall,then if you didn*t bring any white pikmin then go back to the ship and bring them back and break down the wall and call them to you.there you you got perplex pool and yellow pikmin.