adding your images to coco dataset

I have a few images which I want to train with the MS Coco dataset. My model is of Image captioning. But I don't know how to add my images annotations. I have been looking for tutorials and other sources so that I will know how to do it. There are tutorials about Image segmentation etc. But I can't seem to find any about Image Captioning. If anyone is aware of it please help me to understand. So that I can create the annotations more like add them with Coco dataset annotation and start the training.

Kind Regards