Great point! Here are samsung instructions for this.
Download chatgpt from play store (ensure its by open ai and not a scam app). Set it up and make sure you have access to the voice feature
Download good lock from galaxy store (NOT play store)
In the good lock app, In the “life up” section, download the “RegiStar” module.
Open the RegiStar module and click the “side key press and hold action” setting. Turn it on
In the options underneath, choose “open app”. Then scroll to the chat gpt app in the list, and click the setting icon next to the name. Then click “voice”.
Now you should be able to long press the side button to directly access the chatgpt voice assistant.