https://www.theverge.com/2019/3/1/18246255/how-to-re-program-bixby-button-samsung-galaxy-s8-s9-s10-8-note-9

Earlier this week, Samsung released an update to the Bixby app for its Galaxy S8, S9, S10, Note 8, and Note 9 smartphones that finally addresses something we’ve been asking for since Bixby’s debut: the ability to natively reprogram the hardware button on the side of a Samsung phone to do something other than just launch Bixby.

That’s right, you can now use the Bixby button to launch any number of apps, such as the camera, Twitter, Gmail, Google Maps, or whatever you want. But unfortunately, Samsung is blocking the ability to use it for the Google Assistant or other virtual assistants, like Microsoft’s Cortana or Amazon’s Alexa. For that, you’ll still need to rely on a third party app.