You should be able to play pentatonic scales with regular diatonic tuning, just by only playing the strings that are in the scale. So if you tune to C, remember only to play CDEGA for a C major / A minor pentatonic scale.
Are you wanting to tune it so that all the strings are in the pentatonic scale, with no repeating notes and without having to skip any strings? If your harp was made for a diatonic scale, I don’t think you could do that without having the top strings too tight and breaking, and/or the bottom strings so loose they’d sound awful if they played at all.