So a letter to a partner saying ‘you should really try letting me deny your orgasms’?
It’s a bit more complex when it’s the other way around. The submissive will tend to want to feel it’s coming from you, and not just an idea you found online and that you couldn’t introduce yourself and so needed help with.
I think the way I’d introduce it is to just include a little bit of it in your play together, (like the instructions I wrote the other day). See how she responds to it. Tell her you like the idea of not letting her cum, to see how horny she gets and, importantly, how that affects and maybe enhances her submissiveness.
Then try it for a day, if she likes it, try a little longer. At the same time introduce her to some hot denial captions and other women’s experiences. And then just see how it grows from there.
A BIG part of it for the submissive is feeling they are pleasing you by not cumming, so as long as you have fun with it and make it very clear how much you love it and it turns you on, then it’s likely, but not certain, they’ll find they enjoy it too.