The Resolver Record
The Resolver field for an ENS name is normally set to the ENS Public Resolver contract which helps resolve your ENS name into usable records like wallet addresses, avatars, etc.
This is similar to how DNS helps resolve regular domain names into usable records like IP addresses.
There are a wide variety of records that can be set and resolved depending on your use case.
Some examples are:
Wallet address records
Contains records about your various wallet addresses, so that funds can be sent to them.Avatar record
Contains a link to an image stored as an NFT or on a website and used to visually represent your ENS name.Social links
Useful links to, for example, your GitHub, LinkedIn, or Twitter profiles.
ENS Public Resolver
If the resolver is unset or you've changed it you can set it back to the default in the ENS Manager App by going to the ENS name, scrolling down and expanding Advanced settings, and setting the Resolver to the ENS Public Resolver:
The new ENS Public Resolver contract:
0x231b0Ee14048e9dCcD1d247744d114a4EB5E8E63
The old ENS Public Resolver contract:
0x4976fb03C32e5B8cfe2b6cCB31c09Ba78EBaBa41
the old ENS Public Resolver contract will continue to work and should not cause any issues.