I need to import aggregations database from atlas cluster to localhost so i can access it in the future.
If you are talking about this class aggregation db, I think the easiest (if not the only way) is using the MDB Compass UI and export all the collections under aggregations as js files and save it on the local host. Then use mongoimport command in MDB shell and import all the files into a db (of collections) of your choice.
You could use
mongodump as well:
mongodump -u m121 -p aggregations -h cluster0-shard-00-02-jxeqq.mongodb.net:27017 --db aggregations --authenticationDatabase admin --ssl