Recover previous data which are accidentally replaced by new data in few documents in collection

[Dodo Saha]

Accidentally used set method using dart, to insert a new json data into previous json. and now all the previous data are completely removed and replaced by new json. How can I recover those. 

[Dodo Saha]

Actually I use firebase with my flutter application. In a particular collection there were around 450 documents with around 30 key value in each. I need to insert one new key with new value into those documents. I should use update method but due to some bad condition checking logic inside the code the function used set method and all the data replaced by new single key and it's value.