Hi @Anonymous :
If your data source itself does not have an index, I suggest you use the ForAll function.I've made a test for your reference:
My data source:
ClearCollect(YourTable,["Apple","Orange","Pear""Grape","Melon"])
1\Add a text input control-TextInput3
2\Add a button and set it's OnSelect property to:
Clear(Result); /*Result is my custom collection*/
ForAll(
YourTable,
Collect(
Result,
{
No: CountRows(Result) + 1, /*Create a serial number for each record*/
Value: Value
}
)
);
Select the button
3\Add a label control and set it's Text property to:
LookUp(Result,Value=TextInput3.Text).No
This is the serial number of the first searched record.

Best Regards,
Bof