By correcting those who preach them. Paul was warning that when he came to the Corinthians he would boldly correct those who were saying his teachings were carnal and "fleshly." This is how we know it was about confronting false teaching.
2 I beseech you, that I may not be bold when I am present with that confidence, wherewith I think to be bold against some, who think of us as if we walked according to the flesh. 3 For though we walk in the flesh, we do not war after the flesh: 4 For the weapons of our warfare are not carnal, but mighty through God to the pulling down of strong holds; 5 Casting down arguments, and every high thing that exalts itself against the knowledge of God, and bringing into captivity every thought to the obedience of Christ; 6 And having in a readiness to revenge all disobedience, when your obedience is fulfilled.
But now, it is also true that you have to first recognize false teachings from true teachings yourself. If not, you will not know to correct them when conversing with others.
LoL.
Everyone gravitates towards different themes in scripture. Some focus on interpreting everything in light of faith; others in light of knowledge and renewing the mind, or church involvement. I came to the place a few decades ago that the real focus is on the spiritual war between good and evil, and the battle going on between God and Satan for the souls of men, and control over the earth. But like I was saying to SV, we have to win the battles within ourselves first. Satan tries to get in our heads and convince us we are unworthy, or that he will destroy us, or that we will never succeed at serving God. And that's sort of why Paul taught about thinking only on that which was of good report. He wrote that verse from prison but refused to be down. All through Philippians his driving point was to stay joyful, on the principle of how important it is to guard your heart, and stay in hope about what God is and can be doing rather than focusing on what the enemy is doing.
So in a way, both are important. Before you can be effective in the spiritual war going on outside yourself, you have to conquer the enemy within. He wants to silence the truth from being spoken, so if he can keep you bottled up in fears and intimidation then he has accomplished his purpose. The trick is to strengthen your ability to silence him in your thought life. Then you can focus on silencing him in the public arena.