https://www.bleepingcomputer.com/news/microsoft/microsoft-opens-skip-ahead-ring-for-windows-10-redstone-6-insider-builds/

Microsoft announced today that they have reopened the Skip Ahead Ring for Windows 10 Insiders. If you have not had the opportunity to try skip ahead Windows 10 builds or want to join it again, you better do so quickly before all the spots are taken.

Earlier this month, with the release of the Windows 10 Insider Build 17713, Microsoft announced that they were doing a complete reset of the skip ahead ring. This meant that anyone who was currently in the skip ahead ring had been reset to the fast ring, so that when the skip ahead ring opened again it would give others the opportunity to try it out.