Question on mantras

Hi ,I’ve (18M)been learning Hinduism for the past while and been quite interested about destiny.Just a question ,As our past life karmas determine our entire life before we are born which is accurately shown through jyotish how can one change their destiny.Logically speaking we are helpless except to do good for our next life ?So what use do mantras have ,and going to a temple or religious place,praying or meditation as everything is written ?We can only do such spiritual activities to calm our mind but not much more ? What do the scriptures say …?