Fix the preteirite mi hermano (tomar) un café en la mañana.

Mi hermano (tomar) un café en la mañana.

Translation:
My brother (to drink) [blank] a coffee in the morning.

The blank must be filled with tomar conjugated for the subject (mi hermano) in the preterite tense. The subject is third-person singular.
Preterite tense is used to speak about events that happened in the past that have come to an end (not continual actions - those would be imperfect). Thus the sentence must become

     My brother drank a coffee in the morning

in Spanish.

The correct conjugation is tomó.

Mi hermano tomó (tomar) un café en la mañana.

Talk to him translates to "hablale a el" which is a command so there you go