How to install case bearings?

So I am replacing the output cover on a DS90X and there are ball bearing assemblies in the case that are very tight. I bought a heat gun to heat the case and I see in the manual it states to freeze the bearings then install. I was wondering if anyone has attempted this before and if I need a press to install the bearings? I don’t want to break the new cover or destroy the bearings. Any tips would be appreciated.