Hi There.
We are pleased to hear from you, and we apologize if the knobs broke on your cooktop, which does not meet your expectations. We are always here to help.
Refer to the user manual on page 17 about control knobs for your reference: https://downloadcenter.samsung.com/content/UM/202007/20200714112233921/NA5300R_DG68-01132A-01_EN-MES-CFR.pdf.
I also shared this link about "How to Clean your Samsung Gas Cooktop" and scroll to "Knobs and Controls": https://www.samsung.com/us/support/answer/ANS00049945/.
You may contact our Samsung Parts Team at (800) 627-4368, Mon - Fri 9:00 AM - 6:30 PM EST or visit the Samsung Parts website (https://www.samsungparts.com/Default.aspx) if a replacement is needed.
Have a great day.
Melardo