Update the key data type from string to int64

Working with Data
,
3

Hello,

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

But i am getting the below mentioned error:
MongoServerError: Unsupported conversion from array to long in $convert with no onError value

Please help me in updating the query.