how to prep for a big dick?

So I have been talking with this one cool guy, but the problem is he claims he has a dick with a diameter of 6cm (2.36 inches) and needless to say.. I'm scared!

I have lube but are there any other things I could do..? I have a dildo I got for a birthday as a joke, which is 6.5cm (2.55) that I have never used because of how big it is.. perhaps I should 'train' with it first?

well, yeah, a rare problem I suppose but I really want him 😜

edit: I AM sure it is that big, I've seen a photo (with his face on and all) so no doubt about that. it's not what I asked either.