Set Header UD Field based on Detail UD Field

I don't know if this is possible (well, I'm pretty sure it is.  I just can't figure it out).

I have multiple detail records on a quote.  Each detail record has a value in a UD field.

What I want to do, is if ANY of the detail UD field values = "ABC", I want to set a field on the header.  (I don't care if it is a checkbox or a character field, I just need to populate a UD field at the header).  Once the header is populated, I will take action with a BPM based on the header UD field.

Pretty new at this, so I appreciate any help.