How can I schedule 3 years of content in just 9 days?

All you need for this is a social media planner that allows bulk uploading. (Like Radaar)

Then you only have to collect all the messages you want to use in a spreadsheet and upload it to your social media planner at once.

After that you plan the next few days to find / create creatives (Photo, video, carousel, etc.) where you want a creative. Most social media planners have integrated stock photo sites and Canva making this very streamlined.

If you manage to add 100 to 120 creatives in a day, then you'll plan 3 years of daily content in just 9 days.