in mongodb, you do not need to drop any collection just because you have changed a field in your schema. that is how documents databases work; you don’t need a concrete shape to save data.
on the other hand, you need a schema just because the application you use may use an ORM or DAO library to map the data to objects. yet this does not means you need to remove/recreate/migrate all previous data when you have a design change.
your old data still pretty much usable, it is just that your app does not know how to handle the change. for example, you can add a new field “version” to your new document schema to differentiate old and new, and use 2 schema. or you can add both fields in one schema, check for existence of old field but write new data with new field. and if you are the sole user of the data, you can invoke an update to all existing documents from" “id” to “ident”. make note that none of these include a data removal, because mongodb gives all these kinds of freedom.