Hi @Praneeth_Gedela -
You can use the Calculated Fields feature to add new fields computed based on data already in the current context. However you can’t directly bring in data from an external collection using a calculated field.
Instead you should first create a Lookup Field that brings in the external data, then you can create a calculated field that leverages data from the lookup field.
You don’t need to specify either in the query bar, in fact you can’t do $lookup in the query bar.
HTH
Tom