If you are running it from the command line with mn, you can add the parameter --switch ovs,protocols=OpenFlow13
i.e.
mn --switch ovs,protocols=OpenFlow13
if you are running it with a python script, you can pass the OF version in the remote controller:
from mininet.node import RemoteController
from mininet.net import Mininet
from mininet.topo import LinearTopo
c0 = RemoteController('c0', ip=CONTROLLER_IP, port=CONTROLLER_PORT, protocols="OpenFlow13")
topo=LinearTopo(2)
net = Mininet(topo=topo,switch=OVSSwitch,build=False, cleanup=True)
net.addController(c0)
net.build()
net.start()