That insulating material on your refrigerant lines is most likely a Cork Insulation Tape for refrigeration copper tubing. It is a polymer-based material containing butyl rubber, asphalt, and granulated cork (55% by volume).
It is listed for cold and hot applications but I’ve never seen it working well (or for a long time) as a sealing material at the coil compartment wall. It usually sags, separates and opens gaps around the pipe.
If the opening in the air duct is much bigger then the copper pipes, use air duct aluminum tape to make it just the size of the 2 pipes. You can also use HVAC foam tape to make the opening as small as possible.
Another way is to use a piece of sheet metal to make the opening smaller, secure it with screws and additionally tape it along the edges. After that, slide short pieces of additional foam insulation onto the both AC copper lines to make it tighter against that newly attached tape or sheet metal plate.
Use a wire strap to secure it in place (not too tight). If you can still feel some air drafts or have condensation dripping, use silicone between that small piece of a foam insulation and the coil compartment / air duct wall.
Let me know if there’s anything else I could help you with.