tulips need a period of near freezing temps to rebloom. You can let them grow and leaf until the leaves yellow off. Trim everything off, take the tulips out of the pot, let them dry out in a cool shady place for 2-3 weeks then store them in something breathable, (I use an old pair of cotton socks, for 4-6 months, then stick them in the freezer for 6 weeks, thaw overnight and then replant if fresh potting soil. It doesn't aways work, but I have had reasonable success.