"By speaking of a new covenant, God has made the first one old; and anything that becomes old and worn out will soon disappear."

(Hebrews 8.13 GNB)

The "old covenant" was indeed told in the "Old Testament" part of the Bible, but they are not one and the same. The Law in the Old Testament was written to help the Jews live the old covenant, but the Law is not fully obsoleted by the "new covenant" brought about through Jesus. For he himself said the following.

"Remember that as long as heaven and earth last, not the least point nor the smallest detail of the Law will be done away with — not until the end of all things. So then, whoever disobeys even the least important of the commandments and teaches others to do the same, will be least in the Kingdom of heaven."

(Matthew 5.18-19 GNB)

Dear God,
please help me obey you in every thing