Trying to get the router to reserve an ip address for a device

[barrywi]

I have recently bought a Brennan device which stores my music on a hard drive and connects via wifi to an app. The problem I have is that if I leave the machine switched off for a few days the wifi does not connect to it. I do not really understand this but others have suggested getting the router to set a DHCP IP reservation for it . I cannot see or understand how I can do this on the router setup. Can anyone help?

[jamesn123]

@barrywi 

Steps 1-6 on the port forwarding guide should achieve what your looking for

https://helpforum.sky.com/t5/Broadband-Talk/How-to-set-up-port-forwarding/ba-p/2662260