Multiple if or vlookup need help

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Rule	Born	Trigger	Variable
XYZ	Texas	Texan	A or B or C or D
ABC	New York	New Yorker	A or B or C or D
RST		RST	A or B or C or D
WXY		WXY	A or B or C or D
DWF		DWF	A or B or C or D

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Hello I need help with this excel formula. Basically I always have data in Rule column and Variable data. I want Trigger Data as a output.
I have a vlookup setup where there is Born country/data give trigger output but sometimes I do not have born data so that time I have to check Rule+Variable and get output for trigger but i want to do that only for blank Born data and I do not want override already filled Born data. I have over 60k lines of data like this.

Thanks,