This tool merges animator controllers to your avatar's playable layer controllers and syncs to your avatar's expression parameters.

VRCSDK3 version 2021.01.19 or later is required.
Open VRLabs > Avatars 3.0 Manager from the menu bar. Place your avatar in the "Avatar" field within the opened window.
Expand the playable layer to merge on and click "Add animator to merge". Place the animator controller to merge in the "Controller" field.
A suffix is appended to a new parameter if it shares its name with an existing parameter. Modify or remove suffixes as needed.
"Merge on current" merges on the avatar's controller, while "Merge on new" merges on a copy of it. Sync parameters as needed.