Here is a litst of tokens:
https://community.marketo.com/MarketoArticle?id=kA050000000LBvaCAG
But I suspect your fields will be custom fields so you can try your field in the token format or open an email editor and find the exact token and copy it from there.
In your campaigns your smart list should be specific to filter in only records that you want to change then your flow will be a change data value where in the box to the left you will specify the name of the fields that you want to update and in the box to the right you will paste in the token that represent the field from whcih you want to pull the value.
Then when you want to hide the fields afterwards yo can follow the steps here:
https://community.marketo.com/MarketoArticle?id=kA050000000LBvaCAG