IT-Servicedesk - Add button

Hi experts,

I would like to add a customer functionality in our IT-Servicedesk which is based Solman 7.1 SP8 webui.

In fact I would like to create a button directly above or near to categorization-levels.

At clicking on this button, a small popup should appear:

In this popup I would like to have a searching functionality for categories (like on service marketplace selection of a component).

So the user should be able to enter a word and the system automatically finds the correct categorization-levels.

So, does someone know, how to implement first the button and second a functionality like this?
Regarding functionality, this can also be developed e.g. as BSP.

Kind regards