The reason why "Not Secure" is showing is due to your website is being ran over HTTP and not encrypted. To get rid of that warning in the browser, you will need to use HTTPS. To use HTTPS on your domain, you need an SSL certificate for the domain (that SSL certificate basically says "this domain is securing you data correctly to the browser"). Your hosting provider should be able to provide you both these things, you will just need to contact them. Once they set that up, you can follow the instructions here to tell our software to run over HTTPS: