Copying one object's data to another object in same document without manually entering all values

Hi,
This question is for mongoDB version 4.0.0
I am trying to move data from one object to another object.
Example to understand the problem better:
i have a document that is like →

{   
    "name":"$name",
    "value":"$value",
    "object_first_half_info":{
    \\ this can contain up to 300 items
    },
    "object_second_half_info":{
    \\ this can also have about 300 items
    }
}

what i want to do is copy everything i have in “object_first_half_info” to “object_second_half_info”. Basically updating everything i got in object A to B while still keeping everything else same.

So the data should be like:

{   
    "name":"$name",
    "value":"$value",
    "object_first_half_info":{
    \\ same as before
    },
    "object_second_half_info":{
    \\ contains data for before + data from object_first_half_info
    }
}

As i have a lot of fields, i cant do manual work and i have to do this for a lot of documents not just 1.

There are plenty of examples of what you want to do in