Excel's built-in Data Validation feature has limitations when restricting data entry based on another sheet's data. However, you can achieve this using a combination of Data Validation and a helper column:

Here's how to do it:

1. On the sheet where you want to restrict data entry:
- Identify the cell(s) where you want to limit data entry options.

2. Create a helper column (on the same sheet):
- Choose a column next to your data entry cell(s) that won't interfere with your existing data.
- In the first cell of this helper column (let's say cell B1), enter the formula `=VLOOKUP(A1,'Sheet2'!A:A,1,FALSE)`.
- Replace 'A1' with the cell reference containing the value used for lookup.
- Replace 'Sheet2'!A:A with the actual cell range on your other sheet containing the valid data options.
- Drag the formula down to populate the helper column for all your data entry cells.

3. Set up Data Validation:
- Select the cell(s) where you want to restrict data entry.
- Go to the "Data" tab and click "Data Validation" in the "Data Tools" group.
- In the "Settings" tab, under "Allow," choose "List" from the dropdown menu.
- In the "Source" box, reference the helper column containing the valid data options retrieved by VLOOKUP. For example, if your data entry cells start from A1 and your helper column is B, enter `=B1:B10` (assuming you have 10 data entry cells).
- You can check "Ignore blank" if you want to allow users to leave the cell empty.
- Click "OK" to close the Data Validation window.

Explanation:

- The VLOOKUP formula in the helper column searches for the value entered in the data entry cell (e.g., A1) on your other sheet (Sheet2) and returns the corresponding valid data option (if found).
- Data Validation then uses the helper column as the source for the dropdown list, effectively restricting users to choose only the valid options retrieved from the other sheet.

Note:

- This method assumes your other sheet has a unique list of valid data options.
- You can adjust the VLOOKUP formula and cell references based on your specific sheet layout and data structure.