Hi,
Save your "original" string or text whatever you use (textmeshpro, text, etc.) you can use "getTextMeshPro Text" to save your text to a string , then make sure your UI text is empty and now use a loop with "Get String Left" or Right if your are using Japanese or Arabic format
using your saved string with the "Char Count" increasing each loop and store result string and display this one into your empty Ui text zone and don't forget to use "wait" to get a pause between each display if not you'll get your text shown as whole in 0.001 sec...