Power BI - Reset Content Pack Authentication Choice

We have been given a Power BI content pack by one of our suppliers.

In the instructions it said to use Basic Authentication but before I read the instructions I choose Windows Authentication.

Now I can't connect to the dataset, and even if I remove it and try again I don't get the option to re-choose my authentication type.

How can I reset my choice, or make it allow me to choose it again.

I looked at datasets in my settings area but there are no options there for me to change.

Thanks,

Paul