If you would like to appeal from a decision of the First-tier Tribunal, you need to submit an appeal to the Upper Tribunal (Immigration and Asylum Chamber) (UTIAC).
You first need to obtain permission to appeal to UTIAC.
The Tribunal will decide, whether the decision was lawful and whether the Judge had made an error of law, such as a mistake in law interpretation, or overlooked important evidence. If so, it can set the decision aside. In such circumstances, it can either re-decide the matter or send the matter back to the First-Tier Tribunal.