This worked on my LG model, which has a similar control panel to yours:
For front-loading washer dryer combo “Inverter Direct Drive True Balance” LG model #WM3499H*A:
1) Once LG machine is powered ON:
2) Go to the right touch-screen panel, press and hold “Pre-wash + Delay wash” buttons simultaneously for 3-5 seconds. This will turn OFF the CL (control lock/child lock). You’ll hear a little jingle when the function is processed.
3) Similarly, pressing this combo simultaneously again for 3-5seconds will turn back ON the CL .
Hope this helps!