Ahh, ok.
I think if you are talking of a new installation of a plugin you have to create your own list of download URLs or ask dokuwiki.org (that's what the etension manager is doing, see plugin extension).
If you have an existing installation then you can look at the file
manager-dat[/m] in each plugin's directory. This only works for already installed plugins. So I assume this is no working solution for you. The [m]manager.dat file has the following content:
downloadurl=https://github.com/dokufreaks/plugin-folded/archive/master.zip
installed=Tue, 26 Apr 2016 19:38:26 +0200
updated=Tue, 30 May 2017 17:59:37 +0200