How to edit input fields codes in the form?



How do I edit the codes of an input field?

For instance the input field in the unbounce form is this,

Now I want to modify it so it will look like this,

I already spent many hours looking for the edit/modify button for input fields, but I can’t find the button. Or perhaps there is no button or feature to modify the existing codes of the input field?

If I’ll use/insert “Custom HTML” then I will run into multiple sub problems.
And what’s the use of unbounce if I’ll code everything from scratch again?
And my boss can’t modify it easily, If i’ll use the “custom HTML”

Hope someone will give a good advice.

Thank you very much in advance.