By In the early years of the spread of the Gospel of Jesus Christ many people from very messed up lives came to salvation. Their lives changed. Some of the change happened immediately; some of the change came through a long battle against old habits. But the Truth that they heard produced the change in them. Most of them never became a fellow worker of some of the Apostles, but nonetheless, there was a form of ministry that they were all capable of.
Every Christian, simply for believing the Gospel truth, and simply for being changed themselves, are able to teach others the same.
I myself am satisfied about you, my brothers, that you yourselves are full of goodness, filled with all knowledge and able to instruct one another.
Romans 15:14
You might feel a little out of your depth with the complexities of certain situations, and you might feel like you do not know all the verses that famous Biblical counsellors seem to know by memory, but you still know how to identify sinful behaviour, how to show people to Christ for forgiveness, and how to help people do what is right. The knowledge of the Gospel truth that saved you is the truth that will save your friend. The goodness that you have been able to replace your sinful habits with, is the same goodness that will help your friend change. That is why the famous Apostle Paul could write to a group of Christians whom he had not even met yet, and confirm that he is satisfied in their ability to help one another.