Here are the steps to create a dependent drop down list in Excel:
Select the cell where you want the first (main) drop down list.
Go to Data – Data Validation. This will open the data validation dialog box
In the data validation dialog box, within the settings tab, select List.
In Source field, specify the range that contains the items that are to be shown in the first drop down list.
Click OK. This will create the Drop Down 1.
Select the entire data set
Go to Formulas – Defined Names – Create from Selection (or you can use the keyboard shortcut Control + Shift + F3).
In the ‘Create Named from Selection’ dialog box, check the Top row option and uncheck all the others. Doing this creates 2 names ranges
Click OK.
Select the cell where you want the Dependent/Conditional Drop Down list (E3 in this example).
Go to Data – Data Validation.
In the Data Validation dialog box, within the setting tab, make sure List in selected.
In the Source field, enter the formula =INDIRECT(D3). Here, D3 is the cell that contains the main drop down.
Click OK.

I hope this is helps!
Lewis Bert