Horizontal wisdom tooth which has a deep cavity could be treated with either a restoration ( filling) if it has not yet reached the pulp of the tooth or by extraction ( if the tooth is symptomatic ( pain ,swelling ).
Horizontal wisdom tooth often leads to recurrent food lodgement and cavity formation. If it's a recurrent problem it's advisable to extract the tooth as a permanent solution.
Next Steps
consult a dentist , take an IOPA and OPG ( xrays)
go for either a restoration or extraction depending on the findings .
Health Tips
better to manage this at the earliest as further waiting could lead to severe symptoms.