Trouble fixing an old document to work on 365.

Hi There

So a quick brief. A client of mine has an old sheet saved as .xls from 2004 mostly written in VBA. The gentleman who worked on the document has since passed away and took the VBA password with him.

I have been able to convert the document from .xls to .xlsm and broken through the VBA password protection, however the document has ComboBoxes setup which I'm not able to select unless I go through Design Mode.

When I manage to select a box and check the properties, there is no ListFillRange option at all.

How do I resolve this without having to create the ComboBox from scratch?

I appreciate any help and I'm sorry if I can't go further into detail as most of the information on the document is confidential.