Re: How to manually add a value in PowerApps Drop Down
In Employee List Column fields
1) Customer - Look up (Customer List).
Customer SharePoint list only have single column which have distinct customer names
2) Assigned Tasks - Look up (Task List).
In Task List SharePoint List Column Fields
1) Manager Name - Person Data type
2) Customer - Look up Data type from (Customer List)
3) Assigned Tasks - Single Line of Text
4) Assigned To - Person Field.
In Power Apps Edit Form,
Customer data card value => source data is Employee SharePoint List,
Column = Customer, Data type Look Up Column.

Assigned Tasks drop down = source data is "Task List" Share Point List,
Column = Assigned Task, Data type Single Line of Text.

For Example,
In Task List,
Manager Name | Customer | Assigned Tasks | Assigned to |
Manager 1 | Customer 1 | Task 1 | Employee 1 |
Manager 1 | Customer 2 | Task 2 | Employee 1 |
Manager 2 | Customer 1 | Task 3 | Employee 2 |
In customer data card value , when an Employee 1 select Customer 1
In assigned task drop down it list "Employee 1 assigned task for the particular customer + Other option"
| Customer | Assigned Tasks |
When an employee 1 | Customer 1 | Task 1 |
| | Other |
If you need any further clarification, kindly let me know @CNT
Thanks
Pooja-B