@GerardoPlass
So you have one of two choices!
Your formula on the Items is narrowing your entire table to just one column - the COORDINADOR column. So there will be no other columns to use for your .Selected record of the dropdown.
So, one choice is you can get rid of the narrowing and change your dropdown Items property formula to: TB_COORDINADORES
Then you can reference CB_Coordinador.Selected.EMAIL for your TextInput Default as mentioned before.
OR, you can change your Default on the TextInput to:
LookUp(TB_COORDINADORES, COORDINADOR = CB_Coordinador.Selected.COORDINADOR, EMAIL)
Either will work!