Warwick Duo Peugeot

Have you tried looking under the floor on the passenger side of the cab? That's where it is on my somewhat older vehicle (2009) A removable section of the floor

Whatever, here's a no cost option.
1 Remove or lift carpet from pax side of cab
2 If any lift insulation sheet below it
3 You should now see an inset panel .
4 It's fastened with 1/4 turn fasteners undo all of them
5 Remove panel, you should now be looking at the starter battery.

On the +ve terminal will be a big block with many wires attached to it, keep anything metallic away from that. The -ve terminal should just be one wire, perhaps more but nothing like the +ve.

As Don says if you need to jump start look under the bonnet, RHS as you look at if. Just in front of headlight is an exposed bolt, this is the -ve terminal. Just to the left of the fuse box is a small 75mm or so square box, this is hinged, open it, there's another terminal in there, that's the +ve

Fortunately for you I used to write manuals!!!!