i can't put the marble on top of the cabinet

If its custom furniture, choose the furniture and enter the edit interface and apply materials either using the material brush or picking one available from the interface or from something that has been saved to your favorites. HS has a Learn page under Resources:https://www.homestyler.com/learn-help?spm=a1zmxy.20722057.0.0.f46b783cft4Ghd〈=en_US...... or try their YouTube channel with lots of tutorials: https://www.youtube.com/c/HomestylerOfficial/videos......Or just put 'homestyler' in the YouTube search bar for even more tutorials.

If the kitchen is a HS model/uploaded model: click on model and choose 'replace material'. Note that some models may not allow you to change individual surfaces like countertop one color and door fronts another color. You may have to change the whole model. If its a custom model: click on model and choose edit model. In modeling interface choose 'wireface and materials', choose material and then place on surface of model. Or in the design interface you can use the material brush to apply (copy/paste) materials to model surfaces.