Help to find original email to register Lightroom 5

No email required to install software if you have the following:

1. your original media (disks or downloads) you received at purchase and a way to read them,
2. a legitimate serial number for that version, language and platform (Win/Mac) and if it was an upgrade, a qualifying serial number from an older product,
3. an older operating system that can support legacy 32-bit apps.

NOTE 1 : Old installers may not won't work on macOS Sierra, High Sierra or Mojave without terminal workarounds. See the help article below.
https://helpx.adobe.com/creative-cloud/kb/install-creative-suite-mac-os-sierra.html

I'm not positive, but I think that the Creative Suite programs were sold in OS-specific versions. In short, if you wanted to change from Apple to Windows, you had to pay a fee for cross-platforming. I don't think the Apple registration code will work to install the Windows version, assuming you can even get it.

CS is no longer sold or supported. If the above is true, you will not be able to change platforms.

i'm not sure what you're trying to resolve, but you can't "re-register".  you also will cause more problems if you try to use backup files or time machine to reinstall.

you just need your serial number and installation file to reinstall.

if you purchased from, or registered with adobe, you can check your account (using the correct adobe id) for your serial number, https://account.adobe.com

the installation files are here, New Adobe Lightroom 5: Direct Download Links + Difference vs. LR4 | ProDesignTools

follow the directions (esp, step 1)

save the install file. it won't remain online.

thank jim @ prodesigntools.com