First is the Amaize:

This plant can be found in the cave layer of Sylva. The two nearest Amaize plants will be marked on your compass with a yellow resipound icon. When tapped, it will produce resipound. A resipound and sturdysquash sample can be mixed in a Cauldranga to make unknown biofuel.
Next is the Tuberyl:

This plant can be found on Vesania's surface, and will be marked on your compass with a green leek icon. When tapped it will produce leek. If you mix leek and a sturdysquash sample in a Cauldranga, it will make S.O.U.P. Don't forget these plants have a chance of dropping more than one seed, unlike the sturdysquash. You only really need one to get a bunch.

The item that gives the most points is S.O.U.P., so you should prioritize making that. Also, the Cauldrangas on Atrox are the fastest, so you should also use those. (The nearest Cauldranga is marked with a orange plant icon on your compass)Atrox also has the most densely packed sturdysquash, most craters/ravines should have quite a few. The best strategy is to bring a couple of Cauldrangas, leek plants, some storage, and a EXO request platform to a pit with a bunch of sturdy squash. Here's a good example: (sorry if it's not very bright)

Make sure to have storage to load rewards on, and make sure to use the useful rewards too, such as button repeaters and soil and liquid canister. Use the button repeaters to quickly harvest and replant sturdy squash, and use soil and liquid canisters for storing S.O.U.P. If you max out the EXO rocket, you will finish the event within ~5ish trips. Also you will get the 3rd set of computer chips, and be able to get the fourth too.

Since you're in early game, you probably don't want to go to Vesania to get leek plants or atrox for the sturdy squash and Cauldrangas. Don't worry you can do everything (although quite a bit less efficient) on Sylva. Remember the Amaize plants? We'll use those, so make sure to find some. Also look around the bases of mountains for wild sturdysquash and use your compass to find both Amaize and Cauldrangas. Once you get everything setup, it's basically just a bargin bin version of the late game version. Also since you will be making unknown biofuel instead of S.O.U.P., you will need a gas canister to hold it instead.

Thanks for reading this guide, make sure to give it a thumbs up and favorite if you feel like it. Also a person named "Sacha418" helped provide information about the plants, they also made a guide for this event, so check it out too: https://steamproxy.net/sharedfiles/filedetails/?id=3333071043