Hi Joao Costa,
Do you want to display the slider caption look like a given screenshot https://prnt.sc/sl0uix here?
If yes, so please add the CSS code below in Additional CSS Box. Please go to the Appearance => Customize => Additional CSS then paste the CSS here and click to Publish button.
.theme-slider-content .theme-caption-bg.align-center {
text-align: left !important;
}
Let us know if it solved.
Thanks