Find the closest access point ( withe unit that can be round or oblong se pictures) for the box/boxes that are market red. Check if the access point have a blue light.
If the access point doesn’t have a blue light, follow the cable connect and check that it’s connected everywhere.
If the access point doesn’t have a blue light, follow the cable connect and check that it’s connected everywhere.
The cable shall be connected to the router thru either a power adapter or a switch. Check that these are on.
If it have a blue light try to reboot the router se specific guide how to do that.
Reboot the router by pulling in and out the power cable.

How to reboot