At the present time, the IKEA Tradfri smart bulb and plug-in pocket socket work well with smartthings, but there is only partial integration with the handheld buttons and remotes. Many people have been trying to make these work for almost a year. No one has it working yet.
You can add it to your SmartThings network as a “thing“ and then you can use it to control an IKEA Device which is already on your SmartThings network as a parallel means of control. But you can’t make it work for other purposes at present.
It appears that all of the IKEA Tradfri handheld controllers have the same issues.
You might want to take a look at the existing threads and talk to the people there: