How to fix a nasty squeal on a 96 Isuzu Bighorn (Trooper) 3.1 Turbo Diesel?

I have an automatic Isuzu Bighorn (P reg) which runs fine however there is a terrible squeal whenever I accelerate.
The squeal stops when I take my foot off the accelerator and mostly (but not always) it goes away after the first few miles but it is extremely annoying and I’d like to get it sorted.
My guess is it’s something to do with the fan belt.
If someone could tell me how to tighten up the various belts that might be screeching that would be great.
I have no mechanical skills so diagrams would be a plus; if not then very detailed descriptions would be greatly appreciated.
Many thanks,
Jon