In general it is recommended for trans women to start with HRT with small amounts of fat so that any new fat will grow in a female pattern. Reducing fat by eating at a caloric deficit may be a necessary part of transition for some people.
Weight loss correlated significantly with decreases in the circumference of the waist and hips, and decreases in WHR in men and women. At comparable levels of weight loss, men had greater decreases in the waist, and smaller decreases in the hips than women, resulting in greater decreases in WHR. [1]
You can also improve the appearance of WHR by doing exercises targeting muscles in the lower body, in particular the glutes and quads.
Guide on lifting for better proportions: https://www.setforset.com/blogs/news/how-to-get-wider-hips-and-improve-waist-to-hip-ratio
Exercise and a good diet is also a crucial component of maintaining higher IGF levels which will increase the rate at which cells grow and cycle over, giving a greater benefit from the effects of HRT.[2]
It's necessary to eat high amounts of protein[3] to promote healthy tissue regeneration, muscle growth and high IGF which are all important for achieving a more feminine body shape.