Add indicators as any other module - general module loading documentation is also available on the main page of the Highcharts Angular wrapper GitHub repository.
After Highcharts is imported using Highcharts Stock (as a core like in the code snippet below, or as a Highcharts + stock module) use import and initialize the core indicator module first and all needed indicators next (e.g. ZigZag indicator) on the Highcharts variable.
import * as Highcharts from "highcharts/highstock";
const IndicatorsCore = require("highcharts/indicators/indicators");
IndicatorsCore(Highcharts);
const IndicatorZigZag = require("highcharts/indicators/zigzag");
IndicatorZigZag(Highcharts);Example: