You sure can;
In excel simply change the field type and hit save, then load this into Tableau.
In Tableau, you can change the field type on the data load screen by clicking on the little icons at the top of each column of data
Also within Tableau, you can change the field type in the worksheet screen by clicking on the same icons - they are just arranged differently.
I try it in excel file before. I try to change the format to text in Excel. But in Tableau Desktop still in number.integer format.
But now I change the value by adding some word or symbol, can work already.
Appreciate if you could mark the issue as correct/complete in your original post
Now I have another problem.
If I want to replace or edit the current data connection(excel file) with the field's data type integer to another data connection(excel file) but the same field's data type I want is string.
I want to change it before connect to Tableau, therefore the chart created won't affect by it.
I try to change the format in excel, but in tableau did not change. Why?
I've no idea - this is actually an excel issue.
If you are getting errors in Tableau, try sideloading your new data source (add new data source, ensure that the correct settings you need are in place, then click Data > Replace Data Source and replace the old data source with your new data source).
Ok. I get what I want.
Thank you so much Peter