WARNING: This page is about a different car, the 2021 Audi S4 and 2021 Audi A4 Quattro. However, it is still accessible from the selected car via links, so may be relevant.
Fig 1: Removing Outer Jacket Of Insulation
Courtesy of AUDI OF AMERICA, LLC
-- Slide the antenna wire -2- in the mount -3- into the tool head until it stops -1-.