If you have a Heavenly Rift Ticket, interact with NPC Dimensional Vortex on the 1st floor of the Tower of Insolence to get the Heavenly Rift Seeker buff. It will let you teleport on the 14th floor of the tower to Heavenly Rift Guide Arushinai. He will send you to the Heavenly Rift.
In order to get the buff, click on the Dimensional Vortex and choose 'Ask where to find the Heavenly Rift' option. After that select 'Enter the Heavenly Rift', and you will be teleported to Arushinai.
Your Heavenly Rift Ticket must be in your inventory. When you get the buff, it will disappear.
Arushinai can teleport you to one of the three entry points in the Heavenly Rift.
If you die while inside, you can enter again without a ticket. However, you can do it only while the Heavenly Rift Seeker buff is active (it is not removed after death).
When the buff expires, you will be teleported to the 1st floor of the Tower of Insolence.