To configure the dashboard to ensure that selecting a data point on the map only filters the Detail table, you should select Ignore Actions from the context menu of Sales over time. Ignore Actions is a feature that allows you to exclude a sheet from being affected by any actions on the dashboard, such as filters or highlights. You can select Ignore Actions by right-clicking on a sheet on the dashboard and selecting Ignore Actions from the menu.
In this case, you want to exclude Sales over time from being filtered by the map, so you should select Ignore Actions from its context menu. This will make Sales over time ignore any selections on the map and show all values. The Detail table will still be filtered by the map as usual.
The other options are not correct for this scenario. Removing Dashboard Item will delete Sales over time from the dashboard, which is not what you want. Deselecting Use as Filter will disable the map as a filter for any sheet on the dashboard, which is not what you want. Selecting Deselect will clear any selections on the map, but it will not prevent Sales over time from being filtered by future selections. References:
https://help.tableau.com/current/pro/desktop/en-us/actions.htm
https://help.tableau.com/current/pro/desktop/en-us/actions_ignore.htm
On a Tableau dashboard, when a map is used as a filter, it affects all other sheets in the dashboard by default.
To restrict the filter action to only affect the Detail table and not the 'Sales over time' chart, you would modify the action settings. By selecting "Ignore Actions" from the context menu of the 'Sales over time' chart, it will no longer respond to the filtering action initiated by selecting data points on the map.

To split the Customer Name field into two fields named First Name and Last Name, you need to do the following steps:
Open the link to Book1 found on the desktop. This will open the Tableau workbook that uses the Superstore data source.
Go to the Data Source tab at the bottom of the workbook to see the data source page. You will see a table that shows the fields and values from the Superstore data source.
Right-click on Customer Name in the table and select Split from the menu. This will split the field into two fields based on a separator, which is a space by default. You will see two new fields named Customer Name - Split 1 and Customer Name - Split 2 in the table.
Right-click on Customer Name - Split 1 and select Rename from the menu. Type First Name as the new name and press Enter. This will rename the field as First Name.
Right-click on Customer Name - Split 2 and select Rename from the menu. Type Last Name as the new name and press Enter. This will rename the field as Last Name.