Didn't find this with a search but all task effort can be updated by exporting the tasks to Excel, putting numbers in the Effort column, then import the tasks to Wrike.
Note that the import converts the effort to 24 hour days. For example, if 4 is the effort number in the Effort column in Excel for a task, when importing the Excel task into Wrike, the number that will be displayed for the task's effort will be 96 (4 x 24). So to display the imported number as hours, divide by 24. For example, to display 4 hours for effort when the task is imported in Wrike, the value in Effort column in Excel should be 4/24 = 0.1667. Use the formula in Excel then do a Copy > Paste Values before importing since Wrike doesn't like importing Excel formulas.