To get PictoChat on a Nintendo 3DS, you must use homebrew software since Nintendo did not officially include it on the system
Drawing & Text: Includes the classic pen tool, eraser, and keyboard for handwritten and typed messages. Pictochat 3ds Cia
Installation: Obtain a PictoChat .cia file (often extracted from DSiWare) and install it using a tool like FBI. To get PictoChat on a Nintendo 3DS, you
app on your 3DS, navigate to your file, and select "Install and delete CIA." Launch and Chat: Download: Obtain the Pictochat
If you don’t want to mess with forwarders and CIAs, the gold standard for DS gaming on 3DS is TWiLight Menu++ . This isn't a single CIA for PictoChat, but a complete launcher.