@bahaaraan_baran_569
Since many new volunteers did not always asked the CM (channel manager) or resp. language moderator to be put on the team in order to sub and some just went into an editor and did subtitles sometimes in dramas that already had assigned teams, Viki has now blocked the editor to outside volunteers.
If you want to volunteer you have to contact the CM or resp. language Moderator in your case for example German Moderator.
If you look at the main/cover page of a drama it sometimes states under a Moderator/Team(closed) meaning for that language the Team is full.
Even if it states so, sometimes volunteers have unexpected events and must take a break so a team takes gladly
another subber.
Some dramas can be only subbed by QC qualified contributor with experience) or living in a certain region.
Have you tried the Project finder?
http://subber.viki.com/project_finder?utf8=ā&submit_flag=1&type=subtitle&language_code=de&country_of_origin=kr
you might like this one it seems casual and easy there is no German Mod you would need to ask the CM to add you.
https://www.viki.com/tv/32181c-bapmokja-and-haeppy
If you find a drama that needs German subs contact the CM resp the German Mod, he/she can then give you directions about the subbing and a possible googledoc with the parts division etc.
At last checkout my profile with useful links about subbing guidelines and rules I recommend to read first before you start subbing, that will help you to write correctly subs into the box (I see you are very new).
Viel Glueck, pm me on vikimail if you need help (if you want to start seriouly subbing let me know).