Hello,
In March 2021, the support team ended their service which allowed people to manually request relegations to a lower tier -
https://igpmanager.com/forum-thread/42375
However, if you are wanting to race in a lower tier, there are still ways to relegate yourself. If you join a league which has relegation enabled and is coming to the end of their season, purposely retiring from the race or finishing last will mean you are last in the championship and therefore get relegated. I would recommend contacting the league host before you do this as some hosts do not like people joining their leagues just to get relegated.