Magnetic skyrmions and skyrmioniums are exotic magnetic configurations that have several potential applications in Spintronics. In this work, using micromagnetic simulations, we show that it is possible to create metastable skyrmions and skyrmioniums in an isolated cobalt nanodisk, that has as its minimum energy configuration a single domain with perpendicular magnetization. First, we have determined the ground state of the nanodisk and the frequencies of the spin wave modes of skyrmions and skyrmioniums for different values of perpendicular uniaxial anisotropy constant Kz and Dzyaloshinskii-Moriya exchange constant Dint. Next, in order to create a skyrmion or skyrmionium, we have applied an oscillating perpendicular magnetic field with a frequency equal to that of the spin wave modes. Our results show that it is possible to switch from single domain to skyrmion or skyrmionium, tuning parameters such as the intensity of the applied perpendicular magnetic field, and its duration.