AsEnumerable will not be listed, so you just need to type it out. (it’s not case-sensitive also)
It basically converts your table into an ienumerable List of DataRows, so it unlocks all the Array and Lambda functions.
you can use this anywhere you want to use a datatable, like you can use it in an Assign activity to store the result to another variable, or you can bypass the Assignment and use it directly in a For each, to loop through each row.
I will also mention that sometimes your .Where function will not find any rows, which then you will receive a “datatable has no rows” error using .CopyToDataTable. In this case, you might consider using .ToArray instead of .CopyToDataTable and you can check its row count with .ToArray.Count (which you can use as a condition before storing to the datatable or processing that data. EDIT: You can also use an Assign activity to store the .ToArray or array variable back to a .CopyToDataTable after you have checked its .Count… if you prefer.
I don’t think you need further details on where to use it now that I mentioned in an Assign or For each, but let me know if you still need more help getting it to work in your workflow and maybe post a screenshot of your issues with it.