First, we need to know what country you are in, which model of the Samsung smartthings hub you have, and which version of the SmartThings mobile app you are using. Device options will vary depending on these answers.
As @Bry mentioned, if you are in the US, it’s simple. Most of the switches which are sold as individual switches can just be placed side-by-side underneath a cover plate for multiples.
If you are in the UK, there are some triple gang switches made that will work with SmartThings, you just have to check the individual models. But they do look a bit different than the dumb switches.