* Using relationships: You can use relationships to link the secondary data source with the primary data source based on a common field. This will allow you to use fields from both data sources in your visualization without creating new fields or duplicating data. You can then replace references to update the dimension values. For example, you can use relationships to link the updated dorm codes with the primary data source and then replace Dorm_Code with Dorm_Code_New in your visualization.
https://community.tableau.com/s/question/0D54T00000C5ldZSAR/update-data-view-based-on-dimension To update existing visualizations with new codes without changing the field name, using relationships to bring in the secondary data source is appropriate. Then using Replace References allows you to update the references from the old dorm codes to the new ones while maintaining the existing field name.

Explanation:

To combine the tables and meet the requirements, you should use a left join. A left join will keep all the records from the left table (Employeelnfo) and match them with the records from the right table (DepartmentInfo) based on the common field (Department ID). If there is no matching record in the right table, the fields from the right table will be null. This way, you will retain all the records from Employeelnfo, and also include the Department Name, Size, and VP fields from DepartmentInfo. Every record will have a full name because it is a field from the left table. A left join will look like this:
References:
Join Your Data - Tableau
Join Types in Tableau

To calculate the grand total of all the regions, you need to use a Level of Detail (LOD) expression that ignores any dimensions in the view and returns the total sum of sales. The FIXED keyword allows you to specify the level of detail for the calculation, and the TOTAL function returns the sum of all values in the expression. Therefore, the correct LOD expression is {FIXED: TOTAL (Sales)}. Reference: https://help.tableau.com/current/pro/desktop/en-us/calculations_calculatedfields_lod.htm https://help.tableau.com/current/pro/desktop/en-us/functions_functions_tablecalculation.htm#TOTAL

In Tableau, to replace a sheet on a dashboard, you can simply drag the desired sheet (Sheet2 in this case) from the sheets list onto the dashboard area where the current sheet (Sheet3) resides. This action will replace the existing sheet with the new one. Right-clicking and adding to the dashboard adds an additional sheet rather than replacing, and the context menu options mentioned in the other choices are not the standard methods for replacing sheets within a dashboard.