If it's really an Arp, have you tried the Arpeggio Rate slider, upper left corder of a closed Jupiter-8V, near the Arturia logo ?
If it's a Sequencer pattern, you'll need to open the upper section (click "OPEN" on the top toolbar, near the right corner), then select the Modulations tab and then the Sequencer, there you'll have the Rate and the Q: parameters to tweak with.