This CSS will re-style the UL > LI elements that is within the content:
.entry-content ul li {
list-style: none;
position: relative;
}
.entry-content ul li:before {
content: "\26AC";
position: absolute;
left: -1.5em;
color: red;
}
This content: "\26AC";
property is used to set the new icon. This is a standard HTML symbol that is built into the browser. You can change it to any of them listed here:
https://www.toptal.com/designers/htmlarrows/
Or you can use a icon font library if you have one installed.