my friend experienced mangadex april fools ass first time and sent me the image without link, when I tell/told (which do I use here?) him to go back and click on the image he already refreshed the page.
I don't know if it's grammatically correct, but I wouldn't bat an eye if someone used "tell" in that sentence. Only, I will interpret it in a different manner. When using tell, it would seem to me you're saying that you've said the same thing many times over. "My child is lazy and can't study well, but when I tell him off he just doesn't listen." Something like that, although in my example 'whenever' would be more appropriate I believe
Using "told" is definitely the correct tense though, for reasons already said by others. Also, you clearly aren't repeating the same response ad nauseam to your friend's query, just once
Do correct me if I'm wrong, I never formally studied English