Change comment field order

Hi there,

Let's handle one question at a time.

1. Try this CSS:

.comment-form {
    display: flex;
    flex-direction: column;
}
.comment-form #author {
    order: 1;
}
.comment-form-comment {
    order: 2;
}
.comment-form>.form-submit {
    order: 3;
}

Adding CSS: https://docs.generatepress.com/article/adding-css/

Great! Work nicely, added width to changed the length. Is this the right way?

b) How can I add some text before comment name field?
c) How can I add a text in front of published comment name? Refer screenshot

b) This is handled by WordPress itself. You could try something like this:
https://www.elegantthemes.com/blog/tips-tricks/how-to-add-a-message-before-your-wordpress-comment-fields

If not then please check with WordPress' support team.

c) This CSS should work:

.comment-list .comment-author:before {
    content: "By ";
}