Landscape tool not working

I am a beginner and this is my first project, so I am sorry if it’s a stupid question.
I’ve created an island by using Water Body Ocean and everything went fine, but then I realized, that I am unable to adjust the landscape in any way (Sculpt/Smooth/Erase, etc.).
I figured that it is most likely done by a blueprint brush called “Landscape1_WaterBrushManager”.
Whenever I delete this blueprint brush, the landscape edits are working, but it also completely breaks the ocean (The landscape is flat, not curved).
So is there a way to adjust the landscape without having to remove the blueprint brush?

I’d really appreciate any help on this, I am trying to figure out this one for quite some time now.