You can flag down the bus to Higuey just off Las Americas Airport overpass. The bus leaves you in Higuey at the bus terminal for Bavaro.
Another, safer, and more comfortable way, is to get back to the capital, and take a bus from Parque Enriquillo to Higuey and then to Bavaro. Bavaro Express (direct to Bavaro) also stops at Parque Enriquillo at 7.15 am, 10.15am, 2.15pm and 4.15pm. It leaves on the hour from Maximo Gomez st. before stopping at Parque Enriquillo.