You need to select the TOP 1 into a variable in SQL Server. In other words you need to read the first row of a table and for one of the columns in that first row you need to read it and store the contents into a variable.
Normally the code when you are not using TOP is SELECT @myVariable = [myColumn] FROM myTable.
When you are using TOP you need to put that right after the SELECT keyword as shown below.
SELECT TOP 1 @myVariable = [myColumn] FROM [myTable]