will pg_restore overwrite the existing tables?

If you use the --clean option of pg_restore, the old tables will be dropped before the new ones are created.

If you do not use the --clean option, you will get an error message that the table already exists, but pg_restore will continue processing unless you use the --exit-on-error option.

If your goal is to “merge” the existing data in the database and the data in the dump, you may be able to do that if you

• create the dump with the options --inserts --on-conflict-do-nothing options

• ignore the errors you get from the CREATE TABLE statements

• have a primary key or unique constraint on all tables (that is necessary for INSERT ... ON CONFLICT TO NOTHING to work)