Hello. I can understand your concern. Tearing of foreskin while intercourse is not uncommon. It can happen in case if there is a chord of skin adjoining the foreskin to the penis shaft which often breaks during sexual intercourse.
There is no need to be worried a it would heal automatically within a week time. Try to keep the cut a dry as possible and avoid contamination with dirt or urine.
You may clean it with a swab of savlon twice a day. For a week.
Next Steps
Observe for a week. It shall automatically subside. Redness, pus, discharge and intense pain are some red flag signs which indicate immediate consultation from an expert.