I bought that exact one for my drop! Somewhere on reddit I read that Zeal (of Zealios switches) said:

Proper solder plays a big role too. Try to get your hands on some Kester 44 63/37 in either 0.02" or 0.031", or anything in between. 63/37 solder is eutectic which means that it goes from liquid state to solid really quickly, and no mushy stuff in between cooling periods. My iron is always at 650°F with a 3-3.5mm chisel tip.

I know, as I specifically made a note about it and I ordered this with my iron.

https://www.amazon.com/Kester-Rosin-Core-Solder-Dispense-Pak/dp/B00AYJ0B7Y/

or similar will work fine.

I bought this one.

Adjustable, so you know what temperature it is at (assuming it's accurate).

edit: also bought the holder and this is the solder I was refering to.

more edits:

Google tinning the tip (which you should do first) and guide to soldering, some videos/text out there. Watch a couple of videos.