You can click on "File" in the main menu at the top left of the MT4 platform, select "Open Data Folder", then select "Indicators" in "MQL4" and add the indicator you want to add to it.
You can click on "File" in the main menu at the top left of the MT4 platform, select "Open Data Folder", then select "Indicators" in "MQL4" and add the indicator you want to add to it.