Update the key data type from string to int64

Working with Data
,
5

Hello, Thanks for quick response. I tried using the below mentioned query:
db.RetailerRequest.updateMany
(
{“fulfill.tagSerialNumbers”:{$type:“string”}},
[
{$set:
{fulfill:
{$map:
{input:"$fulfill",
in:{$mergeObjects:
["$this",{tagSerialNumbers:
{ $toLong: “$$this”}}]}}}}}] )

Now i am getting the error: MongoServerError: Unsupported conversion from object to long in $convert with no onError value

Please let me know how to proceed further