Yes that is the where part i.e where you added the tags. In most places on forms etc. and in queries a normal <<Tag>> should work but in some places you have to use HTML entities e.g <<Tag>> instead and also tags doesn´t work everywhere (but again should work in most places). Share a screenshot of where you have added it and I can maybe help more.
I see you write class field on form so I guess it is in the config tool settings where I am unsure if tags work (I use custom classes all over and on my forms hence the a bit more general suggestion). Worse case scenario, add a class in the config tool settings and then use that as a selector ("target") for a JS script that add or remove another class. A bit messy though so you can possibly find other workarounds. Everything depends on what you are trying to achieve as the end result (as it can be solved in many different ways).