Unlocking My Passport when Mac is in Recovery Mode

My Passport for Mac backs up once and then not again! Apple customer service is supporting me in sorting out the issue but found that, in Recovery Mode, the external hard drive does not show as being connected - because it is password protected (despite setting the Mac and external drive to ‘always’ talk to each other). Apple has asked me to find out how to unlock, and make available to First Aid, My Passport when the Mac is in Recovery Mode. Any ideas???

Following. I need help too!