Reintroducing my Hamsters?

I have 2 cambell russians from the same litter(unsure of sex). We got one and then a week later got the other one. They both lived quite peacefully for a couple of months. We got them a habitrail ovo tank on sunday but one wouldn't go down the tubes. i left it for a couple of days to see if it would get used to it but eventually i had to lift it down and change the layout of the tank so that it was all on one level. Now the 2 are fighting and the one of them has got a bite on its leg. iv separated them into 2 different tanks for the meantime until the wee hammy heals up but wondered if anyone had any advice on how to introduce them again