That plugin doesn't appear to support splitting the contents of a text file into "lines".
You don't need a plugin to retrieve the contents of a text file; that can be done using the "Value from file/URI" option of the "Set a Text Value" action.
Retrieving a random line, rather than a specific line, can be done using a combination of the "{TXTRANDOM:}" token, and the "Replace with" option of the "Set a Text Value" action.
E.G.
Set text [~textFile] to [C:\text.txt] (Replace '{NEWLINE}' with ';')
Write [Blue] '"{TXTRANDOM:{TXT:~textFile}}"' to log
This replaces the newline characters (on Windows this would be a carriage return followed by a newline, which is what will be returned by the "{NEWLINE}" token on that operating system) with semicolons, which are used throughout VoiceAttack to delimit lists of literal text options.
The "{TXTRANDOM:}" token then takes that semicolon-delimited list and returns one of the entries from that list.
If you intend to use this in a "Say Something with Text-To-Speech" action, you don't need the "{TXTRANDOM:}" token, as that action takes semicolon-delimited list directly, E.G.
Set text [~textFile] to [C:\text.txt] (Replace '{NEWLINE}' with ';')
Say, '{TXT:~textFile}'