You just need to run up to it punch it and it will realise it is mean and will stop you then passive tame him with raw prime meat or kibble hand fed this works every time and I have gotten 3 gigas doing this method
If one is encountered near water, you can simply lure it out to sea with a flyer and it will swiftly drown. Given the water is deep enough. If encountered inland not near water. Pray to the overseers you have something fast enough to out run it. Then promptly die because they're as fast as a mad Hispanic mother with a shoe. Not as deadly as one though.