One time I had a list of mobile phones and I needed to add the country code before each number, so I used Notepad++.
Open the search window by pressing Ctrl+F and select the “Replace” tab, in which we specify what we need to find:
^
And replace with what needs to be added before each line, for example, I indicated:
+38
Below we note the Search Mode: “Regular expr.” and “new line”.
See also my article:
How to add a blank line after each line in Notepad++