In order to unlock tokens one must have a vesting seed or public key of the vesting account and go to https://vesting.bonfida.org
Enter the seed in the search bar and click Search
Once the UI has finished loading the contract an Unlock button will appear
You can find the unlock schedule and transaction history of the vesting account on the Schedules and Transactions details tabs.
Unlocking tokens is a permissionless instruction. It means that anyone can send this transaction to the blockchain, however, the tokens can only be sent to the receiver of the vesting contract. For example, if Alice is the receiver of a vesting contract and that Bob clicks unlock and sign the transaction with his wallet, the tokens that unlock will be sent to Alice because she is the receiver of the vesting contract.
If there is no token to unlock the smart contract will return an error