One step. It's just a rollover from account A to account B, both at TIAA. It will automatically be treated as a conversion as well.
If you are familiar with the generic concept of a rollover (transfer from one IRA account to another, at the same or different custodian), then a conversion is just the name of a specific type of rollover -- from a traditional to a Roth IRA, where some or all of the rollover amount is taxable.
