Step 1: Design a Table of Content include:
H2
H3
H4
H5
H6
...
Add element party width > add headings (H2, H3...) are the same with headings of your blog post. En
Step 2: Scroll down to get Item ID at Gerenal > Advanced:
Step 3: then add this Item ID with prefix # in to this area Geeneral > Content > click Action and Save.