How to delete emails on iPhone?

I was going through my emails and realized I had a bunch of old YouTube notification type emails. I used this method to try to bulk delete them:

https://www.iphonelife.com/content/how-to-quickly-find-mark-delete-all-emails-one-sender-iphone

It seems to work but even after deleting them out of my trash folder they're still in my inbox. I've tried countless times and they won't delete, does anyone know what to do? Or a better way to try to delete them?

Select the emails and click delete