Fitting hard-to-fit tyres:
The warming up advice sounds good. Don't under-rate lubrication. I've struggled for years (if you see what I mean... I spent some of the time during those years doing other things...) to get Brommie tyres back on after fixing puntures, and then I read something on here about lubricating them with talcum powder.
I tried this and instead of a half-hour swearing match, with things thrown and fingernails broken, the tyre just slipped on as if it was no big deal. Almost bewilderingly easy.
Try it.