Acquiring Link Code

I have my account recently registered onto PSO2, but I'm not sure how I can get the link code. Can someone help?

By "link code" do you mean you installed it via Steam and it gives you the popup asking for a code to link accounts + tells you that if you don't do it you're stuck forever with your choice?

The purpose of the link code in Steam on startup is to connect a pre-existing MS Store PSO2 account to a Steam PSO2 account. If you never played the MS Store version, you can just ignore that and pretend it doesn't exist if you're playing on Steam. The MS Store version came out before the Steam version so it was basically a way to just make sure you could still access your old characters, but you can also use it to link an XBox PSO2 account to a Steam one.

If you installed it via the MS Store, there's an option to generate the code in the XBox/MS Store version login menus, but it's only useful if you also have a Steam install somewhere (which you haven't logged in with yet + can input the code). But it's widely advised to stay as far away from the MS Store version as possible because it has a lot of issues.