If you want to use a custom domain, just add it in your DNS settings.

If you’re using the free plan, then you can’t change the subdomain of your site (it’s “yoursite.strikingly.com”). If that’s not okay with you, then Strikingly offers paid plans starting at $9/month which will let you use any subdomain of your choice (e.g., yoursite.com)
https://t.co/RJdZyemwNJ