difficulty – I need to choose the right disk to run my bicoin core wallet

Long time ago I transferred my wallet on My Passport an external hard disk. I have not opened bitcoin core for over 8 months. I opened it 2 days ago, the dialog box opened, which normally doesn’t and I was asked to choose where to open bitcoin core. I chose the external disk.Something went wrong. Finally I understood that there was a problem with the disk and was not mounting on my macbook pro. I fixed that problem. However bitcoin core continues to open at the default file on my mac which is empty. My wallet shows no transactions and it is updating since 11 years back.
I need to be able to open the dialog box at start of bitcoin core to choose again the correct disk but I don’t know how to do that. My knowledge is very limited