I have a duplicate ID in a table.. This is my error:
Item (Magento/Eav/Model/Entity/Attribute/Option) with the same ID 91 already exists.
In which table should i go find this? (Product admin page does not load anymore).
You need to go to database with table name, eav_attribute_option
Now check option_id field within this table and if duplicates row are exist one field need to delete.