I created it that small because i use the actucal size of the cell phone in mm. But maybe i scale bigger.
Ok, for example, i created an extruded circle to cut out the shape of the sensors via boll. difference.

I want to do the same with the speaker. Cutting out a bit of the hull. So i extruded this shape you see in the file and with bool difference i tried to cut it out.
Do you know now what i mean?



Edit:

I added a pic. On which you can see the whole i extruded. I marked also an edge. And i want this edge to be filleted. But this doesnt work. The former curve is also now seperated into a view pieces. I selected all edges and clicked join to get the former shape back. But again fillting it doesnt work.