For this next step, you will need to connect to your website using an FTP client.
Once connected, go to your current theme or child theme folder. You will find it in /wp-content/themes/ directory. Next, upload your custom page template file to your theme.
Now you need to login to your WordPress admin area to create a new page or edit an existing one.
On the page editing screen, scroll down to ‘Page Attributes’ section, and you will find a template drop down menu. Clicking on it will allow you to select the template you just created.