Hello,
I was wondering whether there was any way to remove deleted ticket fields from being visible in filters on Dashboards?
I have Excluded all deleted Ticket Organisation Name's them from a Query;

But they still appear in the first page of the filter in a dashboard that contains the query.

Is there any way of making it, so they don't appear.

A workaround to hide the deleted values from data filters is to create a custom attribute set that will display only the values that you need to show. You can then add this custom set as dashboard filter. You can check out this article for more info: Organizing values by groups and sets.
Thanks Austin!