To undo a 'git add' operation before committing, you can use the following command:

git reset <file>

Replace <file> with the name of the file or files, you want to undo the 'git add' for. If you want to undo all the added files, you can use a period (.) to represent the current directory.

Here are the steps to undo a 'git add':

1. Open your Git repository in a terminal or command prompt.
2. Verify the status of your files by running git status. This will show the files that have been added but not yet committed.
3. Identify the file or files you want to undo the 'git add' for.
4. Use the command git reset <file> to remove the file from the staging area. If you want to undo the 'git add' for multiple files, you can list them all separated by spaces.
5. After running the command, the specified file or files will be removed from the staging area, effectively undoing the 'git add' operation. The files will revert to their previous state before being added.
6. Verify the status again using git status to ensure that the files are no longer in the staging area.

Note: Using 'git reset' to undo a 'git add' does not delete or modify the file itself, but rather removes it from the staging area. The changes made to the file will still be present in your working directory.