Figma allows you to apply smart animate as either a stand-alone transition or by using Smart Animate Matching Layers, which combines smart animate with another main transition.
🅰️ Stand-alone transition
To set as a stand-alone transition, click any connection to open the interaction detail modal and set the animation type to smart animate. You'll also need to set the easing & spring as well as duration properties.
Related: Apply animation type
🅱️ Smart animate matching layers
The plugin doesn't currently support Smart Animate Matching Layers. If used in your design, change to smart animate transition by unchecking the blue box and replacing the main animation type (push in example below) to smart animate.
Related: Replace smart animate matching layers with smart animate transition