Getting a turno for DNI I found to be impossible to do myself.
You have to get a turno for ‘DNI por acto consular’ which you attend at migraciones on Av Antártica. Unfortunately unless you know the name and mail of the woman who gives out turnos it seems no one else down at migraciones knows what to do,
I personally visited migraciones as well as the normal offices for Renaper, phoned several different agencies and used the ‘canal único de contacto’ for migraciones several times and no one managed to get me a turno.
In the end my 12 months visa ran out and I needed to pay a lawyer to get me an appointment, after that was very straightforward,