cd - a shortcut for ‘select -module <name>’

yosys> help cd

cd <modname>

This is just a shortcut for 'select -module <modname>'.

cd <cellname>

When no module with the specified name is found, but there is a cell
with the specified name in the current module, then this is equivalent
to 'cd <celltype>'.

cd ..

Remove trailing substrings that start with '.' in current module name until
the name of a module in the current design is generated, then switch to that
module. Otherwise clear the current selection.

cd

This is just a shortcut for 'select -clear'.