Concatenate string and GUID

assuming you name your fields guid and string then you can concatenate either using a 'Template' field type with template of :
{guid}-{string}
or a 'Formula' field type with formula of:
concat(guid,'-',string)
as in example here: https://www.mockaroo.com/a6f64d60

If you don't want guid and string to appear in your dataset, then rename to __guid and __string (two underscores) and update your formula to refer to the new names.