How can I point a Subdomain to DO server from 1&1 when the domain is already poointed to another DNS.

So i ended up with a very complicated scenario… Please bear with me as i explain.

I had a website on web.com which i built through their website creation app. now i wanted a sub-domain to point DO server but web.com doesn’t let to create sub-domain. so i transfered the domain to 1&1 and created a sub-domain and directed to DO.working ok till then.

but the existing website could not be accessed so i had to point the DNS of domain to dns1.registeredsite.com. But by doing so the subdomain is also pointing to the same and not to DO.

Now how do i point my sub-domain to point to Digital Ocean server. I already have a A record and Cname for the subdomain