custom indicator code

Hi everyone,
I'm here because I need your help:

Last year, I took a very basic course to learn how to write simple code in Pine Script because I wanted to customize my favorite TradingView indicators.

Now, I'm trying to achieve similar results by writing code in cAlgo, but unfortunately, I'm struggling a lot.

Obviously, I have no intention of becoming a programmer, and what I'm trying to do is just create very simple codes, so I hope you'll forgive my lack of expertise.

In TradingView, I customized my RSI by adding these elements to the base code:

• I created variables with values of 80, 60, 40, and 20.
• At 80 and 20, I drew lines to indicate the extreme OverBought and OverSold levels.
• Between 60 and 40, I added a colored fill to highlight the central area of the RSI.

In cAlgo, I noticed that I can manually add levels at 80 and 20, but I can't create the fill between 60 and 40 — or at least, I haven't found any information on how to do it.

But that's not a big issue, as it's just a visual detail.

What I really want to figure out is how to replicate the "plotshape" function from Pine Script:

I want an arrow to appear on the chart when the RSI is above 80 or below 20.

Can anyone give me some advice on how to do this?
Thanks a lot!