Chanit Sutthichit

I started working full time for a restarant and get paid hourly from August - March In April I got promoted and get fixed pay 38k per year. I also do a small amount of freelance work for some side income but get paid per project and not monthly, it's around £700 per project and I have done 3 projects last year and another 2 projects this year. How do I pay tax for my freelance job? Or see what I owe atleast? I have sent a form and also put the details into the HMRC app but nothing has happened. I want to find out how to pay please, if you have an idea how to guide me, it would be much appreciated! Thank you so much!