I uninstalled the existing Huawei Health app and use everything from this webpage (the link came from an Youtube clip).
Files list:
https://mega.nz/folder/xQgFgCSS#gFMrebBNtgILX_Sp4FdNFQ/folder/0N53SIIJ
Youtube:
https://youtu.be/7Z0VKqa5jyY
Do not use the latest Health app as it didn't work for me, just use the Health app from the above link.
My installation order was:
1. Install Taichi app, play a bit with the app's setting to let it update itself (it might happen or not depending on your android version).
2. Install Huawei Health app.
3. Install Huawei Mobile Service app.
4. Install multiple faces app.
5. Close all apps.
6. Open Taichi app, use the + button to "create" the Huawei Health and Huawei Mobile Service. It might take several minutes to finish each task.
7. Use the same + button to manage modules, check the multiple faces module.
If everything is OK you should be able to upload and store your custom watch faces in your GT2.