For example, here are the related videos to show how it works.

Importing Standard Motion

https://courses.reallusion.com/home/iclone/mocap-animation-training?v=iclone-8-tutorial-importing-standard-motion

Auto Import Motion from Known Standard

https://courses.reallusion.com/home/character-creator/characterize?v=iclone-8-and-cc4-tutorial-auto-import-motion-from-known-standard

The more preset of retargeting profiles will be added along with version updates. Users can check the existing presets in your current version of Character Creator 4 by following steps:

1. Apply a non-standard character into Character Creator 4 viewport. In this case, we use the Coyote character in Free resource characters pack.

2. Go to Modify panel, select [Characterization]. (Note: Characterization will be shown if a standard character is selected.)

3. Select [Off] in HumanIK, then select [Load HIK Profile]. All the preset profiles will be listed.

If there is no profile for your external motion, users can make a new one with Character Creator 4. Here are the resources:

Importing Custom Motion

Tutorial Video: https://courses.reallusion.com/home/iclone/mocap-animation-training?v=iclone-8-and-cc4-tutorial-importing-custom-motion

Online Manual: https://manual.reallusion.com/Character-Creator-4/Content/ENU/4.0/09-Import-Humanoid/Saving_Custom_Characterization_Profiles.htm