Convertir negro de cuatricomia a tinta plana

because the printer tells me that the Register Black is a four-color machine.

Hi @isabel_8366 , If you are really only using the Black plate export the PDF to a Gray profile. That will export a single plate (Process Black) PDF:

¡Hola! Isabel,
El impresor te indica que uses la muestra [Negro], no la de [Registro]. El negro de Registro solo se usa para las marcas de imprenta en los bordes exteriores de la hoja de imprenta. El usuario de InDesign normalmente aplica [Negro] a objetos y texto. Si has estado usando [Registro], podrías considerar usar Buscar/Cambiar para buscar objetos con [Registro] y cambiar la muestra a [Negro].

Hola! Isabel,
The printer person is telling you to use the [Black] swatch; not the [Registration] swatch. Regristration black is only used for printing press marks on the outer edges of your printing press sheet. The InDesign user normally applies [Black] to objects and text. If you have been using [Registration], you might consider using Find/Change to search for objects using [Registration] and change the swatch to [Black].