Generally, the mechanism of a knife is at the end of the knife, that is, there is a place at the end of the back of the knife that can be pressed down. Next, at the knife axis, pinch the knife axis up and down with your thumb and index finger at the same time. There is also a switch on the blade similar to that of a wallpaper knife. Press it down or push it up with your thumb. You won’t know the rest until you see your knife. How about you post the brand of the knife and we can find the picture on Baidu.