Depending on the carrier and your Galaxy S7's settings, you may have to enter your SIM card PIN after each reboot. To change / disable SIM PIN on Galaxy S7 (Edge), do as follows:
1. Open the Settings application on your Samsung Galaxy phone
2. Go to the Lock Screen and Security settings (It's under the Personal settings)
3. Scroll down to the Other Security Settings and tap to open it (It's under the Security settings)
4. Under the SIM card lock, open the Set up SIM card lock option
5. Now, to completely disable SIM card lock and turning off SIM PIN code upon booting up, toggle off the Lock SIM card option. (You have to provide your current PIN code)
6. To change SIM PIN on Galaxy S7, tap the Change SIM card PIN option, enter your current PIN code, and then enter the new PIN code.
Note that, you only have 3 attempts to type your current PIN code wrong. After that, your SIM card will be locked and you have to contact your operator/carrier to be able to use your SIM again.