Coolant leak/snapped alternator belt

Start of this year I noticed a coolant leak, at first didn't concern me, but over short amount of time it became worse, whereas instead of having to top it up weekly.
i now found out that any coolant. I now poured in was going straight through to the ground underneath. So thought get it home, though turned out to be very bad idea on my part, as ended up with what recovery driver said was snapped alternator belt due to lack of coolant, then lock down happened so unable to get mechanic to look at it.
spotted mobile mechanic working on customers car round the corner from me, told me he look but had to phone and text my reg and problem, but not heard back so instead have to try to sort all or part of it out myself.

so I need information how to go about replacing alternator belt and fixing coolant leak.