Open Roblox Studion: open it and follow this steps below Import a R15 rig to your workspace and anchor it and use Blender rig Exporter, which I provided at Prerequisites (Install this plugin in Roblox ...

The method used to retargeting animation in addon is shared by Maciej Szcześnik in Unity Connect article "Retargeting animations with Blender 2.80". I made this plugin just to speed up the retargeting ...