Try this :
!pip install -q --upgrade efficientnet-pytorch
!curl https://raw.githubusercontent.com/pytorch/xla/master/contrib/scripts/env-setup.py 2 -o pytorch-xla-env-setup.py > /dev/null
!python pytorch-xla-env-setup.py --version 20200420 --apt-packages libomp5 libopenblas-dev > /dev/null