1. Add a Container Block.
1.1 set Layout > Display -> Flex.
1.2 set the Justify Content -> Center.
2. In the Container Block add a Headeline Block set to P for your text.
2.1 You can adjust its bottom margin.
3. Below that headline add another container block.
3.1 Set its Sizing -> height to 1px and set its Width to what you need.
3.2 Set the Spacing -> Border Bottom to the thickness you want and set all other values to 0
3.3 Set the Color -> Border Color.