You can access it from 'Add' (Plus) button. "Text Mining..." -> "Create N-Gram Tokens".
Select a column that has tokenized text - Set a column that has tokens. This is "token" column if it's tokenized by do_tokenize function.
Select a column as a document - A column considered as document id. If you run do_tokenize beforehand, this can be document_id.
Select a column as sentence id - A column considered as sentence id in a document. If you run do_tokenize beforehand, this can be sentence_id.
Max # of Tokens to be Concatenated (Optional) - The default is 2. Maximum number of tokens to be connected.
Text to Concatenate Words (Optional) - The default is "_". Character to be used to connect ngrams.