Toxic thoughts are thoughts that hurt your inner life. They are thoughts that determine your actions--your behaviour. The Bible states as a man thinks in his heart so is he. Which means you act out your thoughts.
It is possible to rewire your thoughts. The Bible gives you the general parameters . In Philippians 4:8 God though Paul sets them down. "Finally brethren ( first of all it is only being addressed to those who know Jesus as their personal savior from the penalty of sin) whatever is true, whatever is honorable, whatever is right, whatever is pure, whatever is lovely, whatever is of good repute: if there is any excellence and if there is anything worthy of praise, dwell on these things" NASB
In other words, think on God and His work in your life. You are worthy because of what He has done. He is true. He is worthy of honor an so on. Dwell would mean to meditate on Him.
To do a good job of this, one of the steps is to journal. To journal you need someplace to record. You could use your Ipad or a notebook. You need to be able to see your daily improvement and maybe someday turn around and help another.
Feel free to explore your thoughts. Get rid of those toxic thoughts that say you are worthless and are not going to amount to anything. You are worth a whole lot for God to decide to redeem you and someday when He sees you face to face take you home to heaven to spend eternity with Him.