No Developer Mode App in Store

Model is a 43LH576T-TD. There is no Developer Mode app in the store, any suggestions on what to do? AFAIK this is a 2017 model so it has to be something like webOS 3.5. Software Version is currently at 05.00.07. Please help.

The LH57 model is based on NetCast, not webOS. And this model does not support app testing feature. (See Smart TV (LH57) vs. NetCast.) Thank you.