Depending on the material that you have this may work.
I had a motorcycle fairing that broke at the smallest part of the nose cone. I got to the back of the cone, sprinkled some of the powder into a groove, then used an eye dropper to put the liquid onto it and let that set, then did the same again using a piece of fiberglass under the powder. It’s held since.
I don’t remember paying this much for it so check for other sources before purchasing here.
Plast-aid Multipurpose Repair Plastic - 6oz Kit Pool and Spa Repair