If a trainer isn't available, you can manually scan for your budget values:
Advance forward by one day in the Master League calendar to force the game UI to refresh and display your new billions. Benefits of Using a Money Tool pes 2021 master league money tool
Always copy your save folder ( Documents\KONAMI\eFootball PES 2021 Season Update\ followed by your user ID number) before using any tool. If a trainer isn't available, you can manually