Hi @Greggh02,
Thank you for your question and welcome to the Bunnings Workshop community, it's fantastic to have you with us.
As this looks to be either a stormwater, or sewer line, it likely falls under the category of plumbing work that requires a licenced plumber. Before carrying out any work, I would advise you to understand the legal obligations relating to this work in your area.
With this being said, as the elbow joint has been glued into place, a plumber would likely cut the elbow off on either side of the joint and then reinstall a tee fitting using Protek 125ml Red Priming Fluid and Protek 125ml Type N Blue Cement Solvent.
Let me know if you have any further questions.
Jacob
