First, you'll need to buy a domain from a registrar like GoDaddy, pairNIC, Register, or iWantMyName. This usually costs $10-$40 per year. Then you'll need to follow the registrar's instructions to point the domain's A-record (IP address) to 184.73.186.40

Please note that you need to change your domain's or sub-domain's A Record, not its nameservers. And, you don't need to forward or redirect anything, you only need to change the A Record.
Once you've done this, you may need to wait up to 72 hours for the change to take effect. If the domain is set up properly, you should see the your GeniusWiki home page when you visit your domain.

You also need to login your GeniusWiki system admin panel, in General tab, enter your custom domain (ie. "mywebsite.com" ) and "Save".

Once your custom domain is set up, users who visit your GeniusWiki URL will be automatically redirected to your new custom domain. For example, "geniuswiki.mywebsite.com"(sub-domain) or "mywebsite.com"(domain) will automatically redirect you to the hosted GeniusWiki home page.