How can I change the dvd region while I can't click the 'dvd info' on dvd player?

Hi all,

I want to change the region code for a dvd, from code 3 to 1.

I already googled and tried pretty much everything, including the one on Apple Support.

As its instruction, I opened DVD Player and tried to click 'dvd info', but it's just unclickable. I tried to open the dvd that I'd like to change, but the DVD Player said that I can't open it because the file format is not available. (FYI, there is a mp4 and a pdf file in that dvd, is that because of the pdf file?)

Are there any other ways I can change the region code?

Or can anyone tell me how to make the 'dvd info' button clickable?

Thank you.

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