If you are on an embedded network, that means the electrical wiring is configured in such a way that the owner of your building sells energy to all the tenants based there. The owner of a site with an embedded network usually buys energy from an energy retailer and then ‘onsells’ the energy to the different customers at the site. So, unfortunately, you cannot switch your electricity provider and thus won't be able to join Amber.
However, please note: Just because meters are all together in an apartment building does not necessarily mean it is an embedded network. Just send an old electricity bill to email@example.com so we can confirm that for you.