Accidentally changed my character sheet to NPC, how to change it back, please help.

I'm new player and try to modifying my sheet, but it turn out become NPC sheet.. before my try to put some information from compendium, like Constrictor Snake to my sheet, but it turn out I make my sheet character gone and changed to become Constrictor Snake. Can i change it back or i must create new sheet?? I already try to undo the things i do but i didn't fing the way..

The first thing to do is contact your DM and ask them to correct it for you. 

If this is the D&D 5E sheet , there is a Cogwheel icon in the corner, which opens the setting for the NPC sheet. In the bottom-left corner there is a checkbox that says "NPC", uncheck it and your sheet will turn back to a player character. There might still be some data loss.