pls help i cant defeat poseidon cause it has a force sheild

you have to forge the trudent to break the shield you can do this by gathering the three piece from the sea gods cave near daila ankohl ruins near champa, and the temple in the frozen wasteland(forgot the names) and then got to champa and get it forged need any more information fyi you will need parch, burst, and sand. so that means you will at least need to visit aqua rock and gaia rock first before getting the piece in the frozen wasteland

yeah but in the waste land it has a crack how can i broke it

You have to reach the top of tundra tower in order to obtain the burst broach. Equiping this to someone gives you the Burst psynergy, which allows you to destroy cracked objects.

and wheres tundra tower

it is at the most southern part of the map

thanks