Following should help for L2 regularization:
optimizer = torch.optim.Adam(model.parameters(), lr=1e-4, weight_decay=1e-5)
For L2 regularization,
l2_lambda = 0.01
l2_reg = torch.tensor(0.)
for param in model.parameters():
l2_reg += torch.norm(param)
loss += l2_lambda * l2_reg
References: