Basically what vicki said... You will need a small diameter probe. I use a small allen wrench.
I have a single shot adapted model 37. To remove the bolt I:
1. Open up the action as if for loading.
2. Looking down into the action, I insert the allen wrench probe into the small hole I see and press down.
3. While holding the probe down, I pull back on the trigger and slide the bolt out.
While this may sound like a three handed procedure, I am able to remove my bolt with my one and only usable hand.