Have a look at the general approach of writing a model in this tutorial 2.
You could use the PyTorch equivalent methods for the ones you’ve posted, e.g.

Conv1D corresponds to nn.Conv1d in PyTorch

keras.layers.concatenate can be done via torch.cat((a, b), dim=your_dim) in the forward method
Dense corresponds to nn.Linear in PyTorch

Let us know, if you get stuck!