It’s a well used work-horse for TTN so lots of coverage on this Forum* (use search) and in the TTI GW docs and also on the RAK support/documentation site…. search/GIYF!
TL:DR * a good start point is The hard RAK831 cafe part 3 - note early stuff will refer to use with TTN V2 (Sunset Dec 2020) vs current TTN V3 - main difference in real terms is targetting the correct TTN (TTS(Sandbox)) server - where you see target server as e.g. “router.the……” typically change (in your case) to “eu1.cloud…..” based console/server, again search and check the documentation.