In the Plutus Pioneer example in lecture 6, the oracle's UTxO is identified by an NFT. Any transaction that wants to consume this, whether it be a transaction wanting to access the information in the oracle, or whether it be a transaction created by the oracle provider to update the value, would first find the UTxO by looking for the NFT.
If another transaction has consumed the oracle UTxO as an input, it must have created a new oracle UTxO as an ouput. This new UTxO may have the the same Datum, or an updated Datum depending on the reason for consumption, but as part of the transaction constraints, it must also contain the NFT.
The next transaction that tries to consume the oracle UTxO will then find this new UTxO rather than the previous one, as this is now where the NFT is sitting.