Auto Assign MemberRole Upon Sign up

Hi. sorry not very savvy with this type of code. I found a code that seemed to work for someone else. In my case, I have multiple roles. I have Seller, Agent, and Staff roles. My question is, how does the system know which role to assign? Do I need to add something else to the code? See below the code I found.

Can I add a radio button for the user to select which role they are registering for on login? If so, how would I code it?

JSW

import {roles} from 'wix-users-backend';

 export function assignRole(roleId, memberId) {
 return roles.assignRole(roleId, memberId, { suppressAuth: true })
 .then( () => {
      console.log("Role assigned to member");
 })
 .catch((error) => {
      console.log(error);
 });
}

register page code:

import {assignRole} from 'backend/role';
 
 function registerTeacher() {

 let email = $w("#email").value;
 let password = $w("#password").value;
 let first = $w("#fname").value;
 let last = $w("#lastName").value;

wixUsers.register(email, password, {
      contactInfo: {
 "firstName": first,
 "lastName": last
 }
 })
 .then((results) => {
 let roleId="be13f34e-cf4a-4f33-ae7f-c2313d824206";//Teacher roleassignRole(roleId, results.user.id);
    }
     });