I have a BSc in sports studies and have been a self employed personal trainer for 4 years starting from scratch and building it into a profitable full time business. Passionate about helping both personal training clients and personal trainers trying to kick start their careers.
You need to work out what your speciality is for example weight loss or body building and then focus on people that want to improve on that. You can start on social media by doing a free 2 week program and when they see great results they will then go on to continue using your online service whilst also telling their friends and family about you
Do you use any online coaching apps? I recommend trying one and then use Facebook page to attract fans and post the app regularly to get them to see it regularly. Maybe do a month free for the first 10 clients so it gets people through the door then you need to keep them