Percentage Tax Credits on 8% tax rate

hello! we bid services for government agencies kaya lahat ng transactions ko ay may withholding tax, 2% for income payment (1701Q/A) and 3% for money payment (2551q). Plan ko po magswitch to 8% tax rate since di ko naman nadedeclare expenses ko and we only use OSD.

Paano ko po maccredit yung 3% withheld tax? or tapon na yun? (sana hindi kasi sayabg huhu)