Someone may have authority but the fellow may not know how to exercise the authority. Acts 13:8-12 let us know that Apostle Paul exercises spiritual authority over an agent of the devil. Had he not known his authority in Christ, this magician would have turned his preaching into something else.
The Lord isn't pleased when His children choose to use the authority He has given to them.
Moses exercised the authority God gave to him and that put an end to the slavery of the children of Israel. The truth however is that you can't use the spiritual authority you don't possess. If you try to, you would end up spiritually injured just like the seven sons of Sceva.
How can you then exercise this spiritual authority? First, you must have a relationship with the Lord Jesus who has the highest spiritual authority.
Secondly, you must work in alignment with His ways. Just like some people would say nothing good goes for nothing. Once, the disciples start considering why they couldn't use spiritual authority. The Lord simply told them that they had to dedicate themselves to prayer and fasting.
Thirdly, find out and believe true ministers on whom the Lord has given His authority and obey the word of God that comes through the man of God. You too would then start to exercise spiritual authority. A simple God bless you from a man of God with spiritual authority can open the door to huge blessing in your life.