How can i write exception errors to a multiline text field in a SharePoint list from an event receiver

I have a document library on my SharePoint online site, when a user uploads a file in the library a c# itemAdded event is triggered to read the file and store the information in a separate list. This all works perfect. My problem comes in where i need to write any exception errors to a field in the document library. I have a multiline text field in the library already and there are several methods in my code, each method needs to be able to write to the field. How can i do this from the catch method. Any Help would be greatly appreciated.