How do I manually add size on product images
In your shopify Admin panel, under THEMES & SETTINGS section in the left sidebar menu, click on the "Theme setting"
After this, all theme settings page will appear. In the bottom left section "Product images" section available.
In this section you can change product images size by changing image ratio to "Manual".
You can manually add width and height of the images.
Once you done with all settings, Click on the "Save settings" button.
Your settings will be saved successfully.
That's all done.