here are many ways to implement:
HTML element
If you are using the HTML element, You can create a 'Text Input' object and set its Type to 'Textarea', which is the easiest way.And If you want to change its CSS style, you can create a new 'Stylesheet' file in the File Folder.Such as hiding scroll bars, Disable borders, changing text size, font, etc.
Blend mode
You can use the 'Destination out' effect in Blend mode to use a 'Mask' object to block the screen and only display part of the text.
text Mask Scroll Clamped - Example by Federico Calchera
cdn.discordapp.com/attachments/253490735268102144/1068598442294784040/textMaskScrollClamped.c3p
Also, you can use only 1 Mask object to create the effect of a mask, as sub-layers.
cdn.discordapp.com/attachments/225550155531812865/1115557475614216222/MaskTextScrolling.c3p
String Expressions in text
Use 'tokenat', 'tokencount', 'min', 'max', 'mid' system expressions to split the string to implement the text scrolling.And You can find the documentation for these expressions here:Manual - System expressions - Text
Scroll Text - Example by Stan Merezhko
dropbox.com/s/61tfvg3y1b8faby/ScrollText.c3p
Text Scroll Mask - Example by Zackarotto
cdn.discordapp.com/attachments/225550155531812865/923122064955674704/TextScroll-Mask.c3p