I recently made a flat surface and turned it into a rounded shape and sadly forgot on how that was achieved within Blender.
the wished result is on the far right.

I tried to make it now with the "to sphere" function but that gives me really crappy results.
I just know that I haven´t used the proportional editing nor a real sphere back then.

![enter image description here](https://i.stack.imgur.com/3c8cF.png)