How do I change env variables with cmake?

Hi, I have some problems with my build. I can’t run my code in C++ due ot some linker errors (I am using libtorch), which is why I am trying to build my code with the help of cmake. The Problem is, that it does not find Cuda toolkit paths. I don’t even have Cuda on my PC becuase it has no graphics card. So I am trying to set a flag that set the requirement of Cuda to false. The final question is: Where do i set this environment variable in the Building process with cmake?

Selecting Windows SDK version 10.0.17763.0 to target Windows 10.0.17134.
The C compiler identification is MSVC 19.20.27508.1
The CXX compiler identification is MSVC 19.20.27508.1
Check for working C compiler: C:/Program Files (x86)/Microsoft Visual Studio/2019/Community/VC/Tools/MSVC/14.20.27508/bin/Hostx64/x64/cl.exe
Check for working C compiler: C:/Program Files (x86)/Microsoft Visual Studio/2019/Community/VC/Tools/MSVC/14.20.27508/bin/Hostx64/x64/cl.exe -- works
Detecting C compiler ABI info
Detecting C compiler ABI info - done
Detecting C compile features
Detecting C compile features - done
Check for working CXX compiler: C:/Program Files (x86)/Microsoft Visual Studio/2019/Community/VC/Tools/MSVC/14.20.27508/bin/Hostx64/x64/cl.exe
Check for working CXX compiler: C:/Program Files (x86)/Microsoft Visual Studio/2019/Community/VC/Tools/MSVC/14.20.27508/bin/Hostx64/x64/cl.exe -- works
Detecting CXX compiler ABI info
Detecting CXX compiler ABI info - done
Detecting CXX compile features
Detecting CXX compile features - done
Looking for pthread.h
Looking for pthread.h - not found
Found Threads: TRUE  
CUDA_TOOLKIT_ROOT_DIR not found or specified
Could NOT find CUDA (missing: CUDA_TOOLKIT_ROOT_DIR CUDA_NVCC_EXECUTABLE CUDA_INCLUDE_DIRS CUDA_CUDART_LIBRARY) 
CMake Warning at C:/Users/.../libtorch/share/cmake/Caffe2/public/cuda.cmake:21 (message):
  Caffe2: CUDA cannot be found.  Depending on whether you are building Caffe2
  or a Caffe2 dependent library, the next warning / error will give you more
  info.
Call Stack (most recent call first):
  C:/Users/.../libtorch/share/cmake/Caffe2/Caffe2Config.cmake:88 (include)
  C:/Users/.../libtorch/share/cmake/Torch/TorchConfig.cmake:40 (find_package)
  CMakeLists.txt:6 (find_package)


CMake Error at C:/Users/.../libtorch/share/cmake/Caffe2/Caffe2Config.cmake:90 (message):
  Your installed Caffe2 version uses CUDA but I cannot find the CUDA
  libraries.  Please set the proper CUDA prefixes and / or install CUDA.
Call Stack (most recent call first):
  C:/Users/.../libtorch/share/cmake/Torch/TorchConfig.cmake:40 (find_package)
  CMakeLists.txt:6 (find_package)


Configuring incomplete, errors occurred!
See also "C:/Users/.../build/CMakeFiles/CMakeOutput.log".
See also "C:/Users/.../build/CMakeFiles/CMakeError.log".