You have a version that you feel is okay or maybe good? Now it is time for someone else to look at it and share feedback.
Ideally, your reviewer should be someone
Who knows you well
Who knows your work well
Who cares about you and wants your good
Who knows about the opportunity and what they might be looking for
Who will deliver honest feedback about your application
Your reviewer can be your friend, your professor in college, your supervisor or manager at any organisation you have worked. As long as they fit the above criteria, you are good to go.
Unless and until a reviewer does not really know you and your work, they will not be able to offer quality feedback on your application. You are not looking for someone to proofread your application. Instead, what you want is someone to critically read through, tell you about any potential points you may have missed to include, evaluate the authenticity of your application and even give you honest feedback on whether your application is good or not.
A person who does not know you well will only be able to offer surface level inputs on how you should beautify your application. And that is what matters least while you are still trying to fix the skeleton of your application.