Solved

infinite DRS

i dont know if this is a visual bug or affect to the pace but today y were in race and one of my drivers use the DRS with a lap down driver and i see the drs activate all the time i thing he goes faster at the end of the stint but on the pitstop de DRS keep open but in this situation i dont go too much faster

Just visual and usually disappears whenever he next genuinely gets DRS

It's a visual bug, yes.

Was this on the app or on PC?

its on PC

Okay. I think it is a known bug but I'll report it just in case.

How can I use the DRS?

DRS is automatically used by the driver if he is within one second of any car in front of him.