I’m afraid the way it is coded modules contains submodules which contains submodules etcetera… Therefore the parent nn.Module is not aware of it.
Besides parameters is an iterable.
The poor solution is saving the iterable into a  list like:
list(model.parameters())[1]
The elegant solution is filter by name:
for name,param in model.parameters():
    if name == condition:
       do something

The last option is to directly query for it if you know the name:
model.decoder.weight (for example)