I'm a big proponent for washing things! I would wash the felt in cool water with gentle liquid soap like Woolite or Zero and rinse it well. You could block it right away (wet) or let it drip dry first. I often wash second-hand felts for re-purposing them into new hats. You might find the colour comes out in the water a little bit, and there will probably be lots of small felt fibres left in the water too. Don't worry - it will be OK!
Thanks so much for your response. I will give it a try!