Search in Notepad++ looks through text you already have open or through files in a folder. It does not run the program those files describe. This independent tutorial uses the Search menu documented for the Windows editor.
Find in the current file
Press Ctrl+F or choose Search, then Find. Type the text. Use the button your dialog shows for the next match. Leave the search mode on Normal when you want a plain phrase, including characters that a pattern would otherwise treat as special.
Replace
Press Ctrl+H or choose Search, then Replace. Fill in the text to find and the text to use instead. Replace once, read the result, then continue. A replace-all action changes every match in the scope you selected, so try it on a copy when the file matters.
The dialog can also replace in all opened documents. Check that only the files you mean are open.
Regular expressions
Choose Regular expression as the search mode. Notepad++ uses its own expression syntax. A pattern from another editor may need changes. Extended mode is a third choice, for escapes such as newline sequences, and it is not the same as a full expression.
Test the pattern with Find before Replace. If the pattern can match an empty string, do not run replace-all until you have seen the matches.
Find in files
Choose Search, then Find in Files. Set the folder, the file filters, and the text. Review the result list before you replace anything in that folder. Replacing across a project can touch files you did not have open.
The buttons and labels in the dialog are the ones in your installed version. If a label differs, follow the dialog rather than an older screenshot.