From the attached file, it seems that the project tries to use both S32K344 and S32K312 files during compilation, hence the redeclaration errors that are present in the text. I notice that you are trying to build the s32k312_extmode_s32ct model inside the s32k344_simple_s32ct folder. Considering these, my guess is that some artifacts from a previous S32K344 model build are still present and interfering with the files generated by the current model, which if configured for the S32K312 processor. In this case, could you please try and remove the generated folders and build the model again? The generated files include the modelName_ert_rtw, modelNameConfig and slprj folders, the executables (modelName.elf, modelName.bin) and the Simulink Cache file (modelName.slxc).
As a recommendation, you could also navigate directly to the specific folder of the model, I have attached the path to it in s32k312_extmode_simple_s32ct.png, and build it from there. By following this approach, and building models in the folders they are stored, you could avoid this type of issues.
Hope this helps,