Hey there, some schools dont have prehealth advisory board and in that case they will usually ask for letters from professors instead. You should try and ask science professors esp if you did well in a particular class. Also if you plan to ask a professor for a letter, try to get to know him or her through the term of the course so that they'll know you and can write a good letter. If that is not possible you can give a resume or a list of activities that you have been involved in. Another place you can get letters is from work or where you've volunteered. A letter from an Optometrist is good. My School did not have a Pre-Health advisory so I got a letter from the doctor I worked for, two letters from faculty in the sciences at my school, and one from another professor because I knew her very well. Hope this helps and dont hesitate to ask me anything if you have more questions! 🙂
Oh yeah the way you go about doing this is just to ask the professor or person you want if they would be willing to write a letter of rec for you....most likely they will be cool and write it. If they dont want to or have certain conditions, they will let you know. Make sure you do this well in advance so that they have time to write a letter for you. Dont ask like a week before you need it because they might not be able to do it for you since they may have to write letters for other students too. Good Luck!