Recently I needed to update a Magento 2 store to start Order numbers and Invoice numbers to specific numbers. Its pretty easy, you just need access to the database and run these commands:

mysql> ALTER TABLE sequence_order_1 AUTO_INCREMENT=000100999; 
mysql> ALTER TABLE sequence_invoice_1 AUTO_INCREMENT=338990;

Once they have bee executed on the database, the new numbers should start to be used on the next order and invoice that is created.