Qt 5 - How to send data back from child dialog in real time

Qt 5 - How to send data back from child dialog in real time

I have a settings dialog that has some settings that require another
dialog to fully configure. My window shows a preview of the data as it's
being tweaked by these settings. Upon clicking on the configuration button
I launch another modal dialog with some knobs to twist to fine tune the
particular setting.
I wish to send the result of the twisting of the knobs on the child dialog
back to the parent dialog so that it can show the new preview data as the
knobs on the child are being played with. The way I imagine it is I have a
"refresh preview" function in the parent that is called after modification
of it's data preview member variables. The question is, how do I do this?
How can I access getters/setters from the parent dialog as a modal child
dialog? If I do access them will the preview change or will it be blocked
because of the modality of the child?
Thank you!