Click "Customize-Customize Floor" and select the room to enter the customize floor interface. Select the floor and click "Go to Tile Flooring" to enter the tile flooring or paving interface. You can select different tile patterns in the "Pattern" on the left and drag them on the floor. Click the material icon in the right property panel and you could replace the material for each shape.
Once the material replacement is complete, you can also select the wall under 3D view in the General design interface and click "Replace Material" to replace the material.
Attention: replacing the material in the general design interface will overwrite the previous floor tiling.