I've not used the IKEA app, but you add the different light sources to the zones/channels in the HA automations.
Then just cycle through them with the bottom button and the order of the light indicator is the zone.
So zone 1 would be with light indicator in first spot, zone 2 for the second and so on.
This blueprint only seem to have it for one light source, but here's another blueprint where you can set the light sources individually for the zones: