You must re-create the ER diagram based on the changes you made to your database. Workbench does not do this automatically (to my knowledge).
You can create foreign key constraints using the ALTER TABLE
syntax. See the documentation:
InnoDB enables you to add a new foreign key constraint to a table by using
ALTER TABLE
:
ALTER TABLE tbl_name
ADD [CONSTRAINT [symbol]] FOREIGN KEY
[index_name] (index_col_name, ...)
REFERENCES tbl_name (index_col_name,...)
[ON DELETE reference_option]
[ON UPDATE reference_option]