I am fairly certain you can just request it. Just follow the steps below and let me know if that doesn't work for ya!
Locate your handset IMEI number by dialing #06# or go to Settings > More > About device > Status
Write down your IMEI number
Call your service provider’s customer service line and ask for the SIM unlock code for your Samsung Galaxy S5
Provide your Galaxy S5 IMEI number to process the unlock code request
Your service provider will email you the SIM unlock code for your phone in 1-3 days
Remove the back panel from your phone
Remove the battery to access the microSIM card slot
Replace your microSIM card with one from another service provider
When prompted, enter the unlock code that you received from your service provider
Enjoy your SIM-unlocked Galaxy S5 on any GSM network!