Other parties can be created in external documents like issue offering, receive supplies, issue returns and receive returns, the other party which created in IO appear in IO and RR pages, and the other party which created in RS appear in RS and IR pages
As example in issue offering document
Go to the Warehouse module
Open issue offering page
Click new
Close search for customer window
Click on other
Select Please select
Press on 🖉
Insert the name of the other party
Click save