How can I center the page title please?

h1.entry-title {
    text-align: center;
}

To add or override CSS: use the “Additional CSS” option in the customizer.  https://codex.projectdmc.org/CSS#Custom_CSS_in_WordPress or at [site]/wp-admin/customize.php if you don’t have that menu option.

Use the Chrome Developer Tools or Firefox Developer Tools to help you see and test changes to your CSS.

Nice, thank you very much!