Welcome to the forum. This question really should be posted a few forums down in the Auto forum, but I'll answer it anyway. I am assuming that what you have is a swivel bolster, like those made by F. Beltrame, SKM/AB, and AKC. With the knife sitting in you right hand with the firing button and safety facing you depress or push the bolster that is facing you with your thumb from the right. It maybe very stiff but this is how it is done.
If your knife is a picklock, like those made by F. Beltrame or AKC, you have to pick the lock with your thumb or pull on it with your thumb and index finger.
Good luck.