To lookup if a value exists in a range of data in Excel, you can use the VLOOKUP function. Here are the steps:

1. Select the cell where you want to display the result of the lookup.
2. Type the formula "=VLOOKUP(value, range, column, FALSE)" into the formula bar, replacing "value" with the value you want to lookup, "range" with the range of data you want to search in, and "column" with the column number of the data you want to return.
3. Press Enter to apply the formula.

For example, if you want to lookup the value "apple" in a range of data in cells A1:B10, and return the corresponding value in column B, you would use the formula "=VLOOKUP("apple", A1:B10, 2, FALSE)".

If the value you are looking up is not found in the range of data, the formula will return an error. To handle this, you can use an IFERROR function to display a custom message instead. Here's an example:

This formula will display "Value not found" if the value "apple" is not found in the range A1:B10.