Training is not possible for now, the models are available as is.
Currently the machine learning models are pretrained.
Currently available model contains a fixed amount of fields that it can find.
It is supposed to be improved in the future versions though.
Training the models on premises on arbitrary documents capability Uipath is planning for Q1 2020
If you have any kind of ml model you built yourself and would like to train, the scopes you found are perfect for it. But you have to provide your own custom training activity for the model you have built yourself, for now.
To achieve it simply just you can use Export Extraction Results Activity which will return you Dataset(DataTableCollection) and by using index of Dataset you can right it into an excel or csv directly.
Note- Better to use Flexicapture layout approach if you do not wanna create own ML model and so .
use Regex based ML extractor with ML extractor.