How do I add a template suggestion for a Views block?
You need to name your template based on the rules for Views templates.
For example, &quot;views-view--partners--partners--sales.html.twig&quot; would mean:

viewid: partners
view-display-id: partners
fieldid: sales

If this is correct, then all you need to do is clear the cache and reload; the template should be picked up automatically.