To perform the design

Slabs in RCDC are designed for the Imposed Load and Live Load values input for each slab on the Design Data table. These values are imported (along with thickness, etc.) from the slab parameters specified in STAAD.Pro Building Planner mode.

Either:

select the Autodesign tool

or
select Design > Autodesign.

A message dialog opens confirming you want to proceed since the continuity must be reevaluated if you have not already done so.
If you did not previously reevaluate the continuity, click Yes. The Design Output page opens.
A warning message opens stating that two of the slabs have failed the design checks. The same slab is marked with a red row number in the table.
Select the row for the first failed slab (row 13, S24) in the table and then either:

select the Design tool

or
select Modify > Design

or
right-click and select Design from the pop-up menu

The Design Slab dialog for this slab opens at the bottom of the program window.
Type 325 (mm) in the Thickness field in the Design Parameters group.
Select the Design tool in the Design Slab dialog. The slab now passes the design checks.
Select the Accept tool to update the design with the changes.
Repeat steps 3 through 6 for S17 (row 24) with a thickness of 200 (mm).