Without a sample workbook, it's difficult to guide you, unfortunately.
When someone moves to another LOB, do they need to be reported as "newly joined"? If not, it sounds like "Assignment Start Date" is the best indicator of when they should appear as "newly joined".
If you do need to report them as "newly joined" when they move to another LOB, then the fields you described don't sound like they have the information you need. In that case, you'll need to look around for some place where that information does exist, and figure out how to incorporate it into your data; or modify one or more processes (human or technical) to start collecting the level of detail that you require for your report.
Sorry I can't be more help.
I appreciate your response!!!
we need to treat them as "Newly joined" to that LOB and show it in the report.
what type information do i need to gather to fulfill this report.can you please explain it briefly so that i can able to ask to provide.
here i am strongly believing that i need appropriate date field is that true or can we able create this report other than date field?
You are absolutely correct. If you want to report on the date they changed LOB, you need that date in your data source — or you need to be able to deduce that date from the information you already have. It sounds like you cannot deduce the date, so you will need to have the date explicitly captured in the data.