Should I amend my return in this situation?

Filed my return in February. It was accepted and I received a refund. Last week I received a W-2 from a previous employer which I forgot about.  Gross income on that form is only about 1k.  The questions are:

1. Should I amend my return right away or wait to receive a letter from IRS? I'm a little confused because some people say you have to amend it, but than on IRS website it says: "You also usually won’t have to file an amended return because you forgot to include forms, such as W-2s or schedules, when you filed — the IRS will normally request those forms from you."

2. If I have to amend it: Should I only attach one W-2 form that I forgot to report or I have to attach all the forms(even those that I already reported)?

Thank you!