My dog seems to have a nappy rash type of wound?

[Grant]

My dog seems to have developed a kind of nappy rash one patch on the inside of each back leg
I've made a vet appt but it's not for several days
Can I get any advise on what it may be and how I can treat in in the mean time, also he is constantly licking at it which I'm sure doesn't help
I have bathed him in just warm water incase he had sat in something
Thanks