Started Scene on PC, transferred to mac, scene not showing up: Missing reference exception

I started the project on a PC and opened it up on my Mac, but all I'm seeing is empty gridlines, my character controller and a bright magenta tree well beneath the plane. The program seems to recognize that I had a terrain at one point showing up, but in the transfer, the console is telling me that i'm "Missing reference exception: The variable m_TerrainData of 'terrain' doesn't exist anymore. You probably need to reassign the m_TerrainData variable of the "Terrain" script in the inspector." How do I reassign the m_TerrainData variable? Thank you!