It is difficult to help without code to cut and paste into your responders' own notebook. It is advisable to use the code block mark up in the top left icon in this editor.

Among other things, it appears that your import is picking up strings and FindFit is objecting to fitting a model. Check the dimensions and FullForm of data.

Advice. Get commands working in small compact examples. Integrate those parts into a complete working example. Generalize with Manipulate as one of the last steps.