Dear

if i have understand in a right way your question, you need to correct or to increase the bandgap value. there is many correction schemes to do this step. you can try to use MBJ-GGA metaGGA method which can reproduce succefully the band gap value of many wide gap materials. you can also choose the hybrid functionals such as B3LYP, HSE 06 or HSE 03, PBE0, ..and other's.

you can also use the SIC correction.

so, depending on the used code, try one of the listed methods

best regards