After many tries I recommend going for the following strat:
Map settings:
Map Type: Archipelago
John Curtain
No Barbarians
Duel Size
Abudant Resources
Disaster Density 4 (idk if it affects anything)
City States: No City States (for faster gameplay)
Diff: Settler
Speed: Online
Rest is standard.
So, you want to keep rolling initial spawn until you hit the area where the river connects with the sea, with a Stone tile on the coast and with a flatland (/grassland) coastal tile near stone. When you hit that position, hover your cursor over the Flatland tile and check its height above the sea level. You are aiming for 1 meter, if you are impatient, go with 2 meters, but never go with 3 (I failed 7 times with 3m, I gave up on that).
After you settle and unlock Stonehenge, you will see the flood danger on your Flatland tile, it should be white (for 1m) or blue (for 2m). This is the correct setup.
After building Stonehenge, ruch technology to unlock Coal and Coal Factories, since they generate alot of CO2 you need, to acomplish this task. You can also chop all trees/rainforest, to remove some CO2 protection from the planet.
That's it pretty much. Now I will explain you how to track your progress:
On the top left of your screen, you have "Climate" HUD, press it and in the bottom left corner you will see planetary Ice Melt. Those are the events that cause the flood and submerge of coastal tiles. Keep your eye on it and this achievement should be easy to unlock.
The biggest work you need to put is to find suitable starting location, it took me around 20 tries, so don't give up. If you find it and on Settler difficulty, you should be 100% able to get the achievement.