FMIOI and FMIFIIT update by User Exit

Hello Dear Experts.

I need in my FM (BCS) update values in FMIOI and FMIFIIT by some user exit <u><b>before</b></u> the values are written to these tables.

For instance when I open PR I need change value of it (according to my own logic) <u><b>and then write</b></u> the value to FMIOI. The same with FMIFIIT.

Does anyone can advise me which user exits can help me ?

Thanks.