You're looking for a guide on using the money tool in PES 2021 Master League!
How to Increase Salary & Transfer Budget (Tutorial) - YouTube
Input your desired amount for the transfer or salary budget. Apply and Save:
In PES 2021, Transfer and Salary budgets are separate. If you have plenty of transfer money but no wage budget, go to Manager's Office > Budget Settings and set all incoming funds (like competition prizes) to be paid into your Salary Budget.