It will be active by default - no intervention or activation necessary.
If it's not, open PC Settings, then This PC and System - check to see whether a touch panel is listed. If it's not, and it's never worked, the system doesn't have a touchscreen. If the touchscreen did work at some point, but isn't now -- and no changes were made (i.e., the OS wasn't reinstalled), then chances are the touch panel has failed.
May I know if the touchscreen worked before and if it stopped recently? Please help me with the service tag and email address over private message to check if the system was ordered with the touchscreen. Please click my username to send me a Private Message.