Problem with prefabs, help?

Guys,i am having a problem, could you help me? I really don't know what is wrong.

Let me explain: I have a prefab. This prefab has a model inside it, and the model has a script attached that has a variable named "txt". My Canvas' text needs to be inserted in that variable, otherwise i will get an error while in playing mode. I am having a problem, everytime i drag my prefab into the scene, i need to re-insert my Canvas' text to my txt variable in the script for some reason. Now this might sound like something simple that i can deal with, but me and my friend need to change the player model while in playing mode eventually while playing, so if this problem persist the game will bug and i will be ..... Can someone help me? Thanks!