Explanation

Step 1: ALTER DATABASE CURRENT SET COMPATIBILITY_LEVEL
Sets certain database behaviors to be compatible with the specified version of SQL Server.
Syntax:
ALTER DATABASE database_name
SET COMPATIBILITY_LEVEL = { 150 | 140 | 130 | 120 | 110 | 100 | 90 }
Step 2: UPDATE STATISTICS Customers
UPDATE STATISTICS updates query optimization statistics on a table or indexed view.
Step 3: EXEC sp_recompile N' 'Manage_customer'
sp_recompile causes stored procedures, triggers, and user-defined functions to be recompiled the next time that they are run. It does this by dropping the existing plan from the procedure cache forcing a new plan to be created the next time that the procedure or trigger is run References:
https://docs.microsoft.com/en-us/sql/t-sql/statements/alter-database-transact-sql-compatibility-level
https://docs.microsoft.com/en-us/sql/t-sql/statements/update-statistics-transact-sql