How do I convince myself I’m not stupid?

IncidentallyI’m asking here.

Every time I google it everyone keeps telling me to just tell myself I’m not stupid but to be honest that isn’t helping.

I failed/didn’t do as well as I wanted on a handful of different tests and I know I’ll do worse on my resits if I’m not confident but wow I feel dense. Like a bag of rocks. And I’d really like to not feel that way