Spacing block is a very useful block for formatting. As the name suggests, the spacing block can create a spacing between two blocks but apart from that, you can also use two spacing blocks to centre a text block or any other block:
Add two spacing blocks by clicking on the Three Dots icon in the top right corner of the text editor and selecting the option called Spacing.
Drag the first spacing block to the left of the text block or any other block that needs to be aligned centre.
Then drag the second spacing block to the right, in a same way as step 2.
Finally save your changes by clicking outside the text editor until its borders flash blue.
Depending on your page format, you can add just one spacing block or adjust the size of the spacing blocks to achieve the alignment that you want to have.