You can also change the multipliers and use other values instead of 1.272 and 1.618 for Fib extensions.
TradingView has a limit as to how many objects an indicator can create so if you want to go back further for visual backtesting - use the replay tool - it will be able to draw up to the time you selected within its limits.
Let me know if you need anything else...
In true TradingView spirit, the author of this script has published it open-source, so traders can understand and verify it. Cheers to the author! You may use it for free, but reuse of this code in a publication is governed by House Rules. You can favorite it to use it on a chart.