I had the same in the past too, it was gone when I started to do like you with the help of my coach and “Accept it”. Sexual issues are very deep rooted inside us, and you cannot lie to yourself with affirmation or mind trick or something else.
Basically I was going out with a white T-shirt with written on it “I last no more than 5 seconds in bed” and made 30 peoples sign it. Then I was talking about it openly with girls until I accepted it fully. Funny part is that it is ok to last 5 seconds if you can make her come with your fingers or mouths.
Then I don’t know how but it disappeared bit by bit the more I didn’t give a damn about it. I just didn’t put pressure on myself and told myself “I will have great SEX” even if it was 5 seconds. I still had orgasms, and they have orgasms.
When I was around 19-20 yo, I couldn’t penetrate at all because of this ! Sometime I was coming when they putted condom on my penis or during preliminary. Now I last between 5 to 40 minutes. It is not a mind trick, live with it, accept it and when you will be comfortable with it it will be gone. Weird process man.
Good luck to you.