Can someone help me?

@Insanity thanks

@Insanity Yes,

@crowxe RSS is real solar system and REO is realistic engine overhaul, meant for unnerfing engine performance since the stock engines are slightly worse than real life.

@TopSecret2 honestly I don't know what's the problem as I don't know that system nor what's REO

@crowxe That’s a pointless proposition if he downloaded the RSS system and expected to be able to use REO, and was denied that because mods don’t work on iOS. There’s not a lot that can really help him aside from doing two things:
1. Make gigantic rockets
2. Use Methalox and some serious grade LRBs.

Get back to the creator, I guess he should know how to fix his system issues. They usually respond fast

The truth is you really can’t change the ISP to get your craft in orbit around a much bigger planet, especially if you are putting ISP as your priority above thrust and burn time. If anything you have to ask yourself “How do I get enough Delta-V to achieve low orbit around a planet five times larger in radius?”. The short answer to that is to get the vehicle accelerating significantly above a TWR of 1 (where it will be continuously accelerating) without exceeding that TWR until you clear the atmosphere. That is why the first stage is so important and usually employed exactly like it is. Later stages which are fired in vacuum don’t need the additional TWR. That way, the amount of fuel used reduces significantly as you dial down the throttle while using the first stage and over time, the rocket uses more of its fuel towards surface velocity when it finally escapes the atmosphere on a relatively flat trajectory. Another important thing: make sure the gravity turn happens so that you are parallel to the horizon by the time you escape the atmosphere, which enhances that effect.

TDLR: Do not make the ISP your priority when launching into low orbit of any planet, especially when the planet’s gravity, like Earth’s, requires a lot of thrust firing over a long period of time to overcome falling back to the surface.