Hello bk19110254,
as your fluid region is fully enclosed by solid walls, no boundary conditions need to be assigned.
By default, SimScale will assign a no-slip wall boundary condition, which is the right assignment for this wall. So no further setup of boundary conditions is needed for this setup.
In regards to your general simulation setup. As you are using the incompressible solver, please delete all solid parts or your geometry, after the creation of the flow volume. For this application we only need the flow volume.
Best regards
Sebastian