Database
[{"site":"xyz.com","Reg_NumReviews":{"value1":"194","value53":"3,570"},"Reg_Score":{"value1":"3.24","value53":"1.9"}}]
Query
db.collection.update({"site":"xyz.com"},[{"$set":{"Total_reviews":{$sum:{$map:{input:{$objectToArray:"$Reg_NumReviews"},as:"datum",in:{$toLong:{$replaceAll:{input:"$$datum.v",find:",",replacement:""}}}}}},Average_score:{$avg:{$map:{input:{$objectToArray:"$Reg_Score"},as:"datum",in:{$toDouble:"$$datum.v"}}}}}}],{"multi":false,"upsert":false})