How do I fix this?

When I try to join a battle, I get this message saying “Incompatible server version. Please update the client.” Why does this happen and how do I fix it?

They are updating the servers and the game:

.

will i need to do anything after the server work?

Short answer: No, just wait for your game to get the update.

Longer answer:
Once the servers are updated there should be a Client update sent out as well, sometimes that client update is staggered and sometimes it takes a while before everyone gets the client update. How long that will take no one really knows. But looking at the major updates as a comparison then for me personally it usually takes like 20-30 minutes before i get the client update to download and then however long the download and update takes for my client on top of that as well.

I just now got the client update and started downloading so 24 minutes after they started the server update :)