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As I said to make it easier for him just remove the tube completely, lower the shelf if you can or use a wooden bendy bridge as a ramp so he can climb up that way.
You have a Russian hamster & they have furry feet so plastic tubes are very difficult for them even at a less steep angle than the one you have.
Even though he will be smaller than a syrian hamster the cage may still not be suitable, have a look at the ones i mentioned before, unfortunately the cages sold by pet shops are rarely suitable for hamsters.
As the others have said cotton bedding is very dangerous so replace it straight away with some shredded plain white toilet tissue, he will be a bit upset when you remove his nest but will soon make a new one, as i said before put his house on the substrate not on the shelf so he can burrow under it if he wants to.
I don't know if you are aware but Russian hamsters are prone to diabetes, this just means you need to take a little extra care with his diet, a dwarf specific mix like this one is good & no sweet treats, honey treats or fruit.