As commissioner, you can adjust any team's FAAB budget or waiver priority at any time, but it is only possible on the mobile app right now.
The FAAB amounts do not roll over automatically from season to season and it will never reset. The commish has to manually set that as needed.
You can go to your league settings and tap on the commish tab and select the option for "Edit Waiver".
You can adjust those at any time as needed. Keep in mind that the FAAB budget you create at the beginning serves as a maximum. So if you try to manually adjust a team's FAAB and it goes over your initial limit, it will revert.
You'll have to increase that max and then adjust the team's amount. You can increase the maximum in your general settings shown in the photo below: