A coaching bio does not need to be a creative writing exercise, and treating it like one is usually why it never gets written. Most coaches have a strong bio already, they are just stuck trying to sound impressive instead of clear.
Here are a few reliable structures to start from, so you can write yours today instead of putting it off for another month.
Open with the problem you solve, describe your approach in a sentence, then back it up with a credential or a result. It is a simple structure, but it covers everything a prospective client actually needs to know in the order they need it.
A short version of why you started coaching, especially if it began with your own transformation or a specific frustration with generic programming, builds connection faster than a list of qualifications ever will.
If you work with a specific group, say so plainly in the first line. "I help new parents get back into training safely" tells the right person to keep reading and, just as usefully, tells the wrong person to move on.
A bio is a doorway, not the whole house. A few tight sentences that make someone want to see your offerings does more work than a long paragraph that makes them want to close the tab.