Hi @anon21638688 and welcome to the forum!
It sounds like you’re talking about wanting to add a UI element that triggers some action. On that assumption, I’ll answer.
There’s no official way to do it. Asana has no UI component to its API.
There are some folks who have written browser extensions that hook into the Asana UI. Probably the most well-known one is:
which is open source so you can see on Github how he did it.
So you can certainly write a browser extension if you want. Please note, though, that since it’s not supported, Asana doesn’t recommend you do it, and of course they can (and do) change their UI not infrequently and any change can potentially break your extension without advance warning.