We could use Text function in Power Apps to convert any value and formats a number or date/time value to a string of text.
However it doesn't work for lookup column.
As a workaround, change the column type of the looked up to single line of text instead of number type.
This window basically is asking for more information to get filed value from a SharePoint List.
Data source: The list/library you are trying to access and get information.
Field from source: The column you try to access.
Return filed as: Just like it says, you can choose the type (date, string, integer) of the value you get from the column in data source....