In a previous post we create a new legal entity. The next step in setup would be to initialize the number sequences for that company and review them as needed. You can manually create number sequences but you might want to first start with the wizard to populate them all and then go back and adjust the ones you need to adjust.
Here is a quick overview.
D365FO Update3 (7.0.4307.16141)
Cheers
Lachlan