There is no General_Prompt_SurveyStartedDate variable. There is a COLUMN/FIELD of a table called that but that is different than being its own variable.
Try this:
fileName = 'exampledataset.xlsx'
exampledataset = readtable(fileName)
newColumnValues = exampledataset.General_Prompt_SurveyStartedDate; % Extract one column.
newColumnName = 'CopiedDate' % Give it a new name - whatever you want.
exampledataset = addvars(exampledataset, newColumnValues, 'Before', 'General_Prompt_SurveyStartedTime', 'NewVariableNames', newColumnName);
