To Loosen
To Relax
transitive verb, ichidan verb
緩む is "to loosen," but has to do with loosening on its own. This word is when you loosen or relax something, meaning to loosen or to relax.
The reading comes from 緩む, so you can use that!
どうぞネクタイをお緩めになってください。
Please feel free to loosen your necktie.