Download and set up the plugin.
Motion Manager can be installed either via the aescripts + aeplugins manager (recommended), or manually.
C:\\Program Files\\Maxon Cinema 4D RXX\\plugins\\/Applications/MAXON/CINEMA 4D RXX/plugins/Replace RXX with your installed Cinema 4D version (for example, R25 or 2024).
If the plugin does not appear, double-check that the folder name and nesting are correct (the plugin folder should be directly inside plugins/), and ensure you restarted Cinema 4D after installing.