HELP DNS cloudflare

I just received an email to change the DNS, I have 4 server names with dns and ip, and they want me to change to 2 dns, deleting the others, but my query is, that ip I put these DNS, it is not allowed to put the empty field (ip).
what ip do they go?

Hi @camilo.zavala.c,

You can determine the IP addresses of your Cloudflare nameservers following this tutorial:

Ready and I will change it, and I put the ip that they gave me with your url !!, thank you very much, what do I have to do? just wait or something else?

If you have changed your nameservers to point to Cloudflare, you will need to wait for propagation and the zone to activate on Cloudflare.

I have not changed anything, I have this configuration from a long time ago, from time to time the web falls, when I log in.