I then installed OpenZeppelin Contracts 2.5 to a buidler project
$ npm i @firstname.lastname@example.org
With the buidler etherscan plugin installed I then verified:
$ npx buidler verify --network goerli 0xAF53B91508003D6875b00Da470808f2dB53F1A5E
Successfully submitted source code for contract
contracts/YelmiToken.sol:YelmiToken at 0xAF53B91508003D6875b00Da470808f2dB53F1A5E
for verification on etherscan. Waiting for verification result...
Successfully verified contract on etherscan
I also verified on Ropsten, which I assume you had deployed to, so your token will now be verified.
Download truffle flattener
Create a folder whit truffle
Copy your contract code
Flatten your contract code
Copy your flattened contract to etherscan or othwerise .its done