The town centre hotels have limited, or in some cases no, parking. Those further afield have large car parks.
The best place to park in central Warwick is the Cape Road Car Park which is free of charge and has no time limit. This is about 100 metres along Cape Road on the right heading north from the A425 (Northgate). Closest postcode is CV34 4LB.
Otherwise there are plenty of council car parks, which are detailed here:
https://www.warwickdc.gov.uk/info/20547/warwick_car_parks
There is unrestricted street parking anywhere south of Temple Grove along the A429 (Stratford Road) which is a 10-15 minute walk from the venue. Alders Grove normally has plenty of spaces.