Config enable sharding collection in MongoDB cluster
You can enable sharding on collection base, i.e. collection T3 is sharded.
Unsharded collection are created in the Primary Shard, see Sharded and Non-Sharded Collections

Sharded and Non-Sharded Collections
A database can have a mixture of sharded and unsharded collections. Sharded collections are partitioned and distributed across the shards in the cluster. Unsharded collections are stored on a primary shard. Each database has its own primary shard.

Typically the Primary Shard is the least loaded shard at the time when the database was created. When you are not happy with the selected Primary Shard then you can move it with movePrimary command. But you have to move all collections of one database, you cannot move a single collection.
db.adminCommand( { movePrimary: &lt;databaseName&gt;, to: &lt;newPrimaryShard&gt; } )