I don’t know if there are tools to convert the TF model automatically to PyTorch and think you would have to rewrite it manually in PyTorch.
A definition of a custom model can be found in this tutorial 365 and might be a good starter.
Once the model architecture is created in PyTorch, you could convert the pretrained weights from TF to PyTorch. @tom and I did the same for the StyleGAN model in this notebook 483 so you could take a look at the implementation.