Sending messaing to another process

Hello everyone,

I’m working with library BPMN model, in case of requesting book and the book is not available, the requested the manager gets requester details and entered him to waiting list,

So, if there is any message that has been display in specific process, can I display or sending this message to requesters in waiting list? For example the message 'the book will return will be returned in delay of 48 hour (2 days), how can I sending this message to all requesters into waiting list and if I check there runtime/history variables result I can see the message into their variables list?!