Manufacturer Layout
If you do not see modules assigned to Manufacturer layout, go to Design > Layouts > Manufacturer and make sure route is set to product/manufacturer% (note the % at the end of it) and that should solve the issue.
If you do not see modules assigned to Manufacturer layout, go to Design > Layouts > Manufacturer and make sure route is set to product/manufacturer% (note the % at the end of it) and that should solve the issue.