In order to form the negative past form of る-Verbs, you will need to remove the る, and then follow it with the auxiliary verb ない (or ます), conjugated into their past forms. This will either be なかった (casual), or ませんでした (polite).

• 今朝（けさ）ニュースを見（み）なかった。
  I didn't see the news this morning.
• ゴミを捨（す）てませんでした。
  I did not throw the trash away.

A semi-polite form may also be used. This is constructed by using なかった, and then simply adding です. This form is not grammatically correct, but is so common that most sources (and native speakers) would consider it correct.

• ライトが消（き）えなかったです。
  The light did not turn off.