Yes just like Evangelion said it is under Appearance -> Body Modification -> Body -> Upper Body
It should appear under waist width
If you can only see waist width (and not breast size) it means this individual is not feminine enough (not full sissy yet)
Check Estrogen and Testosterone level under status -> health (testo should be 0 and estro 100)
First, you need to convince this individual to take both anti-androgen and estrogen hormones
To do that, you need to play the betting game and your winning must be start HRT
Next, you need to make them take both hormones daily under schedule until said percentage is reached.
When they grow breasts naturally (randomed between A-C) then you can change it to A-F
It might take a several weeks to reach said percentage. Make sure you have enough money for the journey.
And start skipping time fast. I recommend installing chastity cage before skipping for it also takes a lot of time.
It is easy to win money with betting in this game because it is rigged (you always win if you play correct)
Just gain karma like I mentioned
HERE then find very rich clients and bet big bucks.
Alternatively, make a very rich client your sissy and activate the "you belong to your master" brainwash.
Sissy mode has similar approach.
It is a very long process but if you like sissies the result is glorious and very satisfying and pretty much worth it.
There are also other aspects. Just have fun with the game. Test stuff. There is no time limit.
This is a very grindy and complicated game. It is also extremely buggy and gets more bugs each update. If you like it, give it a few years to cook. And if the dev doesn't abandon it, it might be something.