Sometimes I'll just resume where I was. But for two months off I'd knock some arbitrary amount off (like 20%) and start again with a ramp at your earliest convenience. If you notice it too easy or two hard it'll quickly become apparent if your FTP is off in either direction, assuming you're doing Base of some sort and not trying to do VO2s or some shite.
Sometimes I'll just resume where I was. But for two months off I'd knock some arbitrary amount off (like 20%) and start again with a ramp at your earliest convenience. If you notice it too easy or two hard it'll quickly become apparent if your FTP is off in either direction, assuming you're doing Base of some sort and not trying to do VO2s or some shite.