You can create a function that will allow you to do this with any text, simply set a variable called "dialogue" before you call the function and it will display the text in the action bar, for example:
Set Variable (dialogue = "Hello!") >> Call Function(Action Bar Text)
Then, make a function called Action Bar Text.
Function(Action Bar Text) >> Player Action: Send Message(dialogue)
If you've set this up all correctly, when you join the game and trigger the call function then a message with "Hello!" should be sent in chat.
Next up, creating the actual system. Firstly convert the text to a list using Set Variable: Split Text(diagList, dialogue, (/txt [])), using the /txt [] trick Prince mentioned. Then get the length of that list using Set Variable: Get List Length(lLength, diagList). This will tell us how many characters are in the text. So all in all, you should be left with:
Function(Action Bar Text) >> Set Var: Split Text(diag List, dialogue, "") >> Set Var: Get List Length(lLength, diagList)
We'll have to use a Repeat: Multiple Times to achieve that scrolling effect. Set up a Repeat: Multiple Times(i, lLength) with a Control: Wait(1) in it. Then we'll trim the original text we're given so that only certain characters are shown, using Set Var: Trim Text(toSend, dialogue, 1, i). This will set toSend to the trimmed version of dialogue, which has been trimmed to the characters between 1 and i. This means that the first iteration will be 1 and i=1, so toSend will be set to "H", second iteration will be 1 and i=2, so toSend will be set to "He", etc. Finally we just send this as an action bar using Player Action: Send Action Bar Message(toSend). Here's what your code should look like:
Function(Action Bar Text) >> Set Var: Split Text(diag List, dialogue, "") >> Set Var: Get List Length(lLength, diagList) >> Repeat: Multiple Times(i, lLength) [[ Control: Wait(1) >> Set Var: Trim Text(toSend, dialogue, 1, i) >> Player Action: Send Action Bar Message(toSend)]]
Or you can always grab a template from the code vault.
Apologies for the wall of text, I wanted to explain the system in full. If you have any further questions or critiques of my system then feel free to let me know :) Hope this helps!