If you are learning spanish and need that they speak slowly to you so you can understand you have to ask:

-Puede hablar un poco mas despacio por favor
(Could you speak a bit more slowly please?)

If what you need is that they repeat the sentence then it is like this:
-Podria repetir por favor? (polite)
-Puedes repetir por favor? (colloquial)
(Could you repeat please?)