Export 'x' photos from Apple Photo app?

I have a major task ahead where I want to / need to export a huge lot of photos from this app and onto an external disk, for safekeeping. As it is each run will likely come up wit a differrent number. so my question is:
how can I specify in the macro that 'x' can be any number??? Any help/suggestions will be appreciated.
I have just taken a screenshot, it is in danish, but should be easy to understand/ convert to english: