In order to split folio, you must have two folios,
1) To create new folio open room >> Folio summary tab >> New Folio.
2) Once its done go to the Rate information tab click on letter “S”.
3) If you want to split it equally just select equally and software will automatically split charges equally, if you select manually then you can insert the charges manually as per the folio.
Related Question: Is it possible to create two seperate invoices for room tariff & extra charges in a same room?