If the SD card was changed to "Internal" rather than the standard "External" storage, things should automatically save to the card. However you have to be running at least Android "Marshmallow", be running a phone that the manufacturer hasn't restricted the option on, and use the instructions I am including here to change it to "Internal". If that was not done, then it wouldn't make the card "Internal" storage.
Now, you can, without the card being made "Internal", save photos, music, etc., to the card (just not apps). All you have to do for that is to change the setting in the individual app (camera, browser, etc.,) to save those file to the card. Or, if they are files being put on the device from say a computer, then you would just...