You don't have to worry about the LOR. When the professor writes it it'll get uploaded to optomcas and the WHOLE application including the LOR will get sent to the schools you choose. You do not have to worry about the addressing.
It's pretty sad that you have no idea how optomcas works yet and ask questions about everything. If you get accepted to any legit school please let me know so I can drop out if their standards are that low.