'Replace Tee with Collar' tool replaces the selected TEE with a collar and a reducer
In this example we will change TEE with Collar - Reducer pair. 

Select TEE to be replaced with Collar - Reducer pair

Notice the TEE we are going to replace is of eccentric type.

An appropriate reducer gets  placed at outlet1 and inlet Duct gets stretched so that it gets joined to reducer. Branch Duct is stretched in the direction of main duct and a Collar is added in between them.