For this part. I’m using Hello Child Theme as an example

Step 1: Download the Hello Child Theme (Hello Theme + Hello Theme Child DOWNLOAD HERE)
Step 2: Go to the site dashboard. Hover on the Appearance then click Themes

Step 2: Click Add New. Then Upload Theme

Step 3: Drag your zip theme file or Choose File from your download folder. Then click Install Now

Step 4: After the Theme installed successfully. Click Activate