Speaking evil is saying anything that God did not say. If you love life and want to see good days, then take control of your words. Train your tongue to speak what God said. Don’t speak foolish words when your enemies/unbelievers are around you.
There is power of life and death in your words. Speaking wisdom brings health to your life. Your faith and words should go together. When problems are around you, watch your words.
So, in order for your tongue. Mouth to speak life, God needs to touch/cleanse it and it’s done through salvation.
Once your tongue is sanctified, then train your tongue to speak what God says. God has given us a new tongue. That is the gift of speaking/praying in tongues, so let the Holy Spirit speak through you and edify yourself.