I had a fear of oxers until recently. I’d suggest starting with smaller oxers, such as ones at cross rail and low vertical heights and just practice those untilyou feel comfortable. Then gradually raise the height and width of the jumps, getting comfortable over each size. Don’t push yourself too hard that you completely lose confidence over them but push yourself a little bit so you are able to work through it. I hope this is helpful and good luck!
Hi Maeve, perhaps start small, narrow, and square, even to the point of it looking like a vertical. Keep riding to where you feel comfortable, moving higher and wider slowly as you start to feel more confident. Instead of focusing on the jump, keep bringing your mind to the job at hand, especially when approaching. Wishing you all the best in overcoming this fear! It can be quite tough, but you are making progress just by the fact you are searching for a solution!