You can sign a petition supporting UN membership for Taiwan at this place.
This is a letter by the chairman of German Bundestag's Berlin-Taipei parliamentary amity circle, Wilhelm Josef Sebastian, to the UN General Secretary supporting Taiwan's UN entry bid.
I made the following comment on signing the petition for UN membership:
I fully support Taiwan to regain its rightful place at the United Nations. In my opinion, the international community must not exclude a democratic country as vital and distinguishably sovereign as Taiwan, above all not for economic reason. The UN goals of democratisation and liberation ought not succumb to the veto of one single security council member! The Taiwanese people have all rights in the world to self-determination.