Database
[{"key":1,"INFO":"A=5242;AF=987;C=82622"},{"key":2,"INFO":"A=5242;AF=987;C=82622"}]
Query
db.collection.aggregate([{$project:{INFO:1}},{$set:{info_arr:{"$split":["$INFO",";"]}}},{$set:{info_arr2:{"$map":{"input":"$info_arr","in":{k:{$first:{$split:["$$this","="]}},v:{$last:{$split:["$$this","="]}}}}}}},{$set:{info_obj:{"$arrayToObject":"$info_arr2"}}},{"$replaceRoot":{"newRoot":{"$mergeObjects":["$$ROOT","$info_obj"]}}},{$unset:["info_arr","info_arr2","info_obj"]}])