I've just tried this with the latest MangledVerb and H9 Control on iOS 12.1.4, and preset import seems to work fine. First, please confirm that you have the latest of the apps installed (in the App Store under "Updates"
After that, did you follow these steps?
- In the MangledVerb app, export your User Presets using the "Export" button.
- Open the Files App, and copy all MangledVerb presets from the MangledVerb folder to the H9 control folder
- Open H9 Control