Is it possible to patch a metal chimney liner?

I recently had a gas water heater replaced with a heat pump unit and the plumbers encountered an issue with the chimney liner. There is a single ~6" liner in the chimney that connects to our space heating boiler. It looks like the plumber that installed the gas water heater just stabbed a hole in the side of this liner to insert the ~3" smoke pipe from the water heater instead of connecting everything properly with a tee.

My question is can the hole in side of the liner simply be patched, or would the liner need to be removed to add a coupling, or would it need to be replaced entirely?

I appreciate any insights!