I don’t ride cross country, but I recently started training a horse to be a jumper, after I hadn’t ridden in many years. So I had not only my confidence to get back, but hers to create. Brick boxes freaked her out at first so to let her know the boxes weren’t out to get her, I would walk her around them at the start of our ride to let her see them, in hand and once I was in the saddle. I also talk to her while riding, stuff like good girl, that jump isn’t scary, let’s try again, I count strides out loud. It lets me burn off my nervous fearful energy and keeps her engaged.
Doing a lot of non-riding work, like grooming and in hand exercise are also good ways to build trust and confidence. The horse gets to learn that you aren’t going to suddenly go crazy and you learn what the horse likes and is comfortable with, and the areas that need work because they are less comfortable. And it is okay to take a step back, maybe do different, less scary jumps to build up confidence then start working the scary ones back in. Riding is about having fun and when you aren’t having fun anymore, something needs to change to make it fun again. Work at a level you are comfortable with and when you feel ready, take a step forward.