I tried multiple times in the past to land on Cylero. After my recent succesful attempt to land on it which was done with the Pheobe Lander, I realized why I failed the first couple of times. I didn't slow down enough before entering the atmosphere. If you are stuck in the same place as I was for a year or so, Here's a quick guide on how to land on mars.
Build or select a launch vehicle that at least has 10.5km/s of delta V
Launch the rocket when Droo and Cylero are around 44º degrees apart from each other on their respective orbits
Get to LDO (Low Droo Orbit) and set a planned burn around the line of twilight for a transfer to Cylero.
Once your burn is done, warp to the interaction with Cylero's SOI.
Set a second planned burn at the periapsis of your fly by of Cylero and wait until you are in your desired orbit.
Use the Hohmann transfer to lower your orbit until it is around 350 km - 120 km.
Deorbit your craft
when you get close to the atmosphere burn your engine until your speed is around 120 m/s - 290 m/s
seperate your lander/rover
ignite your landers engine and set your throttle to 100%
Lower or raise your throttle depending on your speed and altitude at your own course of guidance.
Touchdown! Congratulations you have (hopefully) landed on Cylero!
If you don't know how to do Hohmann Transfers, here's a quick and simple video:
https://www.youtube.com/watch?v=pJHluGiM5X4
(Copy and paste this link to your search box)