roof tile slipped - cost to reseat

[shd1970]

Hi there,

I have noticed that one of my roof tiles has slipped out of place meaning that i can see the felt underneath

Can anyone confirm approx how much i should be expecting to pay to have it fixed please ?
(worcestershire)

Also, is there any way of knowing other than getting up there as to whether it was nailed and has corroded, or whether they are just laid and thus, i could perhaps just push into place from the edge without having to go on the roof myself ?

Thanks in advance